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PubMed1989

Histone H1 in two subspecies of Chironomus thummi with different genome sizes: homologous chromosome sites differ largely in their content of a specific H1 variant.

Chromatin of Chironomus thummi (Diptera) contains seven sequence variants of histone H1. A structurally divergent H1, variant I-1, accounts for about 20% of the total H1 in C. th. piger and for about 30% in C. th. thummi. Monoclonal antibodies against this protein have been induced and have revealed its restriction to the centromeres and to a limited number of other bands in the salivary gland chromosomes. Indirect immunofluorescence of the somatically paired homologous chromosomes of F1 hybrids indicates that the difference between the two subspecies in H1 I-1 content largely depends on differences situated at a number of distinct homologous chromosome bands. These bands were intensely decorated by antibodies against H1 I-1 in C. th. thummi but appeared virtually black in C. th. piger. The same bands, however, were decorated equally in both subspecies by an antibody that reacts with other H1 variants but does not recognize H1 I-1 and by a polyclonal anti-H1 antibody. The results suggest that H1 variant I-1 is characteristic of a specific type of chromatin that is confined to distinct chromosome segments and that is more frequent in the subspecies C. th. thummi, which has a 27% larger genome.

Animals↗
PubMed1992

The dermal-epidermal junction of human skin contains a novel laminin variant.

We report the identification of a novel laminin variant that appears to be unique to a subset of epithelial basement membranes. The variant contains two chains electrophoretically and immunologically identical to the B1 and B2 chains. Epitopes contained in the laminin A chain are absent from the molecule, and a 190-kD chain substitutes for the A chain. V8 protease analysis and Western blotting studies indicate that the variant 190-kD chain shows structural and immunological similarity to the 200-kD chain of kalinin. Rotary shadowing analysis indicates that the 190-kD chain contributes a large globular structure to the variant long arm, but lacks the short arm contributed to laminin by the A chain. The variant is produced by cultured skin explants, human keratinocytes and a squamous cell carcinoma line, and is present in human amniotic fluid. Polyclonal antibodies raised to kalinin, a recently characterized novel component of anchoring filaments, and mAb BM165 which recognizes a subunit of kalinin (Rousselle et al., 1991) cross react with the variant under nonreducing conditions. Immunohistological surveys of human tissues using the crossreacting antikalinin antiserum indicate that the distribution of this laminin variant is at least restricted to anchoring filament containing basement membranes. We propose the name K-laminin for this variant.

Basement Membrane↗
PubMed1982

Identification of a new Venezuelan equine encephalitis virus from Brazil.

Two strains of recently isolated Venezuelan equine encephalitis (VEE) complex virus from southern Brazil, avirulent for 6- to 8-week-old mice and short-haired guinea pigs, were characterized by biologic, serologic, and biochemical means. They were shown serologically to represent a single, newly recognized variant of subtype I. Two-dimensional polyacrylamide gel electrophoresis (PAGE) of ribonuclease T1 digests of viral ribonucleic acid showed considerable homology between the genomes of the new variant prototype and variant IA. Three structural proteins were visualized by discontinuous sodium dodecyl sulfate-PAGE (SDS-PAGE). Although the smallest protein of both recent isolates migrates with the capsid proteins of other subtype I viruses, the larger structural proteins of the new variants differ in molecular weight from the E1 and E2 envelope glycoproteins of the other subtype I variants. The new isolates produced peptide fragment patterns that were identical to each other, but different from the patterns of other subtype I viruses, following SDS-PaGE of dissociated virions digested with Staphylococcus aureus V8 protease. Since these two isolates were from Culex (Melanoconion) species mosquitoes and from a bat (Carollia perspicillata), were postulated that this is an enzootic VEE virus variant for which the classification IF is suggested.

Animals↗
PubMed1990

Carbohydrate structures of a human tissue plasminogen activator variant expressed in recombinant Chinese hamster ovary cells.

The carbohydrate structures of a genetically engineered human tissue plasminogen activator variant bearing a single N-glycosylation site at Asn 448 are reported. After isolation of the tryptic glycopeptide and liberation of the N-linked carbohydrates by polypeptide:N-glycosidase F, 6 major oligosaccharide fractions were separated by HPLC on NH2-bonded phase. Their structures were determined by compositional and methylation analyses combined with fast atom bombardment mass spectrometry. Seventy percent of the carbohydrates were of the biantennary complex type with fucose at the proximal GlcNAc and zero, one or two alpha 2-3 linked NeuAc. The remainder were triantennary structures with one, two or three NeuAc.

Animals↗
PubMed1999

A structural and transcription pattern for variant surface glycoprotein gene expression sites used in metacyclic stage Trypanosoma brucei.

African trypanosomes first express the variant surface glycoprotein (VSG) at the metacyclic stage in the tsetse fly vector, in preparation for transfer into the mammal. Metacyclic (M)VSGs comprise a specific VSG repertoire subset and their expression is regulated differently from that of bloodstream VSGs, involving exclusively transcriptional regulation during the life cycle. To identify basic structural and functional features that may be common to MVSG telomeric transcription units, we have characterized the anatomy and transcription of the telomere containing the ILTat 1.61 MVSG gene. This telomere contains pseudogenes of the ESAG1 and ESAG9 families found in bloodstream VSG transcription units. The 1.61 MVSG occupies a monocistronic transcription unit and is transcriptionally controlled through the life cycle. The 1.61, and also the 1.22, MVSG transcription initiation site sequences resemble eukaryotic initiator elements. Sequence comparison reveals that four out of five characterized MVSG expression sites have a conserved region 2.0-4.7 kb long upstream of the MVSG. In some cases, this region contains not only the transcription initiation site that we have observed to be active in fly-transmitted trypanosomes but also, upstream, another sequence, described elsewhere as a 'putative promoter' for the MVAT set of M/VSGs (Nagoshi YL, Alarcon CM, Donelson JE. A monocistronic transcript for a trypanosome variant surface glycoprotein, Mol Biochem Parasitol 1995;72:33-45). In fly-transmitted trypanosomes, the latter element is transcriptionally silent. Our analysis of the structure of MVSG telomeres suggests that metacyclic expression sites arose from bloodstream expression sites.

Animals↗
PubMed1990

Structural analysis of human apolipoprotein A-I variants. Amino acid substitutions are nonrandomly distributed throughout the apolipoprotein A-I primary structure.

In the course of an electrophoretic mutation screening program of 32,000 dried blood samples from newborns, 17 genetic variants of apolipoprotein A-I (apoA-I) were found and structurally analyzed. The following defects were identified by the combined use of high performance liquid chromatography, time-of-flight secondary ion mass spectrometry, and sequence analysis: Pro3----Arg (1 x), Pro4----Arg (1 x), Asp89----Glu (1 x), Lys107----0 (4 x), Lys107----Met (2 x), Glu139----Gly (2 x), Glu147----Val (1 x), Pro165----Arg (4 x), and Glu198----Lys (1 x). The distribution of point mutations in the apoA-I gene leading to these 9 and 11 other variants of apoA-I reported previously was statistically analyzed. Substitutions are overrepresented in the 10 amino-terminal amino acids (p less than 0.001, chi 2-test) and in residues 103-177 (p less than 0.025, chi 2-test) or residues 103-198 (p less than 0.05, chi 2-test), respectively. We further noted the following. (i) Prolines were substituted by arginine or histidine residues at a frequency much higher than expected on the basis of random nucleotide substitutions (5 out of 18 "electrically non-neutral" amino acid substitutions, p less than 0.001, chi 2-test). These substitutions are the result of transversions of cytosines contained within stretches of at least 5 consecutive cytosines in the apoA-I gene. The observed hypervariability of the apoA-I amino terminus, therefore, might be caused by a hot spot for mutation formed by the 7 subsequent cytosines in codons 3, 4, and 5. (ii) CpG dinucleotides were overrepresentatively affected by C----T transitions (5 out of 18 electrically nonneutral amino acid substitution, p less than 0.001, chi 2-test). The hypervariability of the apoA-I alpha-helical domain might therefore be caused by CpG dinucleotides predominantly occurring in codons 120-208 of apoA-I (82 out of 125). (iii) Comparison of mutation sites in the human apoA-I gene with sites of nonsynonymous substitutions revealed that amino acid substitutions found in human apoA-I were predominantly localized in areas that were little conserved during mammalian evolution. These regions may therefore represent areas of less structural constraint for the function of apoA-I.

Amino Acid Sequence↗
PubMed2000

Differential mRNA expression of the two mineralocorticoid receptor splice variants within the human brain: structure analysis of their different DNA binding domains.

In human brain tissue, cortisol action, at basal concentrations, is mediated by the mineralocorticoid receptor (MR). An in-frame insertion of 12 bp in the MR-DNA-binding domain due to alternative splice site usage between exons 3 and 4 results in an MR mRNA splice variant (MR+4) encoding a receptor protein with four additional amino acids compared to the wild-type MR protein. To elucidate the questions of sex, age, and/or tissue dependent differences of the relative amount of the two mRNA subtypes, we examined 131 fresh human brain tissue samples from temporal and frontal lobe or hippocampus. One hundred and twenty samples were obtained from patients with epilepsy and 11 samples from patients with brain tumours. A small but significant difference of the MR+4 mRNA splice variant proportions in cortex (9.5 +/- 0.8%) and subcortical white matter (6.6 +/- 0.7%) of the temporal lobe could be detected, indicating differential MR splice variant expression within these brain areas. Moreover, the splice variant ratios in samples of the temporal lobe cortex collected from patients with epilepsy differed from samples of patients with brain tumours. These data point to an altered expression of the MR splice variants in epilepsy, and strengthen the supposition of a tissue specific alternative splicing of the MR mRNA. The frequent occurrence of the MR+4 transcript raises the question of its functional significance. For this reason, an MR+4 DNA-binding-domain structure model was generated by computer-based homology modelling based on the known glucocorticoid receptor structure. The data obtained revealed no distorting effect of the inserted four amino acids on the adjacent secondary structures, thereby suggesting that both zinc fingers retain their function. The resulting structure of the MR+4 model leads to the supposition that the receptor retains its function. Moreover, databank analysis with respect to this kind of steroid receptor variation and our own sequence data of the closely related progesterone receptor sustained the hypothesis that only corticosteroid receptors were affected by this alternative splicing event.

Adult↗
PubMed2002

Boar salivary lipocalin. Three-dimensional X-ray structure and androsterol/androstenone docking simulations.

The X-ray structure of variant A of authentic boar salivary lipocalin (SAL), a pheromone-binding protein specifically expressed in the submaxillary glands of the boar, has been solved and refined at 2.1 A resolution. The structure displays a classical lipocalin fold with a nine-stranded sandwiched beta barrel and an alpha helix. A putative glycosylation site, at position 53, has been found to carry a GlcNAc sugar residue. In contrast with what was expected on the basis of mass spectroscopy reports, the internal cavity was found to be devoid of bound pheromonal compound (androstenone or androstenol). Instead, a small electron density volume could be satisfied by a glycerol molecule, a component of the cryoprotecting liquor. The internal cavity was revealed to be very small for steroid compound accommodation. Therefore, docking and molecular dynamics experiments were performed with both pheromonal compounds. These simulations clearly demonstrate a volume increase of the cavity upon steroid binding and the adaptation of the amino-acid side chains to the steroid molecules. This explains the higher affinity of SAL for both steroid molecules compared to other smaller molecules, although no specific interaction is established with either compound.

Amino Acid Sequence↗
PubMed1990

Epithelial integrin alpha 6 beta 4: complete primary structure of alpha 6 and variant forms of beta 4.

The integrin alpha 6 beta 4 is a heterodimer predominantly expressed by epithelia. While no definite receptor function has yet been assigned to it, this integrin may mediate adhesive and/or migratory functions of epithelial cells. We have determined the complete primary structure of both the alpha 6 and beta 4 subunits from cDNA clones isolated from pancreatic carcinoma cell line libraries. The deduced amino acid sequence of alpha 6 is homologous to other integrin alpha chains (18-26% identity). Antibodies to an alpha 6 carboxy terminus peptide immunoprecipitated alpha 6 beta 4 complexes from carcinoma cells and alpha 6 beta 1 complexes from platelets, providing further evidence for the association of alpha 6 with more than one beta subunit. The deduced amino acid sequence of beta 4 predicts an extracellular portion homologous to other integrin beta chains, and a unique cytoplasmic domain comprised of greater than 1,000 residues. This agrees with the structures of the beta 4 cDNAs from normal epithelial cells (Suzuki, S., and Y. Naitoh. 1990. EMBO [Eur. Mol. Biol. Organ.] J. 9:757-763; Hogervost, F., I. Kuikman, A. E. G. Kr. von dem Borne, and A. Sonnenberg. 1990. EMBO [Eur. Mol. Biol. Organ.] J. 9:765-770). Compared to these structures, however, the beta 4 cDNAs that we have cloned from carcinoma cells contain extra sequences. One of these is located in the 5'-untranslated region, and may encode regulatory sequences. Another specifies a segment of 70 amino acids in the cytoplasmic tail. Amplification by reverse transcription-polymerase chain reaction of mRNA indicated that multiple forms of beta 4 may exist, possibly due to cell-type specific alternative splicing. The unique structure of beta 4 suggests its involvement in novel cytoskeletal interactions. Consistent with this possibility, alpha 6 beta 4 is mostly concentrated on the basal surface of epithelial cells, but does not colocalize with components of adhesion plaques.

Amino Acid Sequence↗
PubMed2001

Endothelin gene variants and aortic and cardiac structure in never-treated hypertensives.

BACKGROUND: The polymorphism of several candidate genes has been studied in relation to essential hypertension and cardiovascular complications. Target organ damage in essential hypertension is a complex disorder influenced by multiple genetic and environmental factors. The possible contribution of endothelin gene variants to target organ damage in hypertension in humans has not been studied in depth. PROCEDURE: We assessed the influence of genetic variants of components of the endothelin system ETAR -231A/G, 1363C/T, ETBR 30G/A and endothelin-1 (ET-1) 138insertion/deletion (I/D) on aortic stiffness, left ventricular geometric, and radial artery parameters in 528 never-treated hypertensive subjects of European origin. The study population included 314 men and 214 women with a mean age of 48+/-0.5 years (+/-SEM). In samples of patients, aortic stiffness was assessed with carotid-femoral pulse wave velocity (PWV). Radial artery thickness was measured with an echotracking angiometer and left ventricular geometric parameter with standard echographic procedures. RESULTS: The main results showed that the ETAR-231A/G (P = .022) and the ETBR 30G/A (P = .026) receptor gene variants influenced PWV level in women. The -231G and 30G alleles were associated with a codominant increase in PWV, explaining 18.6% of its variability (P = .005). In men, the ETBR 30G/A receptor gene variant was also related to the level of radial artery parameters (P = .02). No association between the 138I/D polymorphism of the ET-1 gene and left ventricular and radial artery parameters was observed in either men or women. CONCLUSIONS: These results indicate that the influence of endothelin system genes can be detected first on arterial parameters.

Adult↗
PubMed2001

The glycan structure of albumin Redhill, a glycosylated variant of human serum albumin.

Although human serum albumin is synthesized without carbohydrate, glycosylated variants of the protein can be found. We have determined the structure of the glycan bound to the double-mutant albumin Redhill (-1 Arg, 320 Ala-->Thr). The oligosaccharide was released from the protein using anhydrous hydrazine, and its structure was investigated using neuraminidase and a reagent array analysis method, which is based on the use of specific exoglycosidases. The glycan was shown to be a disialylated biantennary complex type oligosaccharide N-linked to 318 Asn. However, a minor part (11 mol%) of the glycan was without sialic acid. The structure is principally the same as that of glycans bound to two other types of glycosylated albumin variants. Glycosylation can affect, for example, the fatty acid binding properties of albumin. Taking the present information into account, it is apparent that different effects on binding are caused not by different glycan structures but by different locations of attachment, with the possible addition of local conformational changes in the protein molecule.

Carbohydrate Sequence↗
PubMed1986

Reduced affinity for thyroxine in two of three structural thyroxine-binding prealbumin variants associated with familial amyloidotic polyneuropathy.

T4-binding prealbumin (TBPA), a protein synthesized by the liver, circulates as a tetramer and transports 15-20% of T4. We studied 3 variants of the TBPA monomer recently identified in serum and amyloid fibrils of patients affected by familial amyloidotic polyneuropathy (FAP). They represent single amino acid substitutions at positions 30 (type I), 60 (Appalachian), and 84 (type II). Tests of thyroid function and the apparent association constant (Ka) of T4 binding to TBPA were measured in whole serum from 14 carriers of FAP identified clinically, by amino acid sequence analysis, or by DNA restriction fragment analysis. Significant reduction of Ka was found in subjects with FAP types I and II, but not in subjects with the Appalachian type. Mean (+/- SD) values of 0.24 +/- 0.08 X 10(7) M-1 for type I and 0.26 +/- 0.10 X 10(7) M-1 for type II were significantly (P less than 0.0001) lower than those for normal relatives (1.39 +/- 0.30 X 10(7) M-1) or unrelated normal subjects (1.41 +/- 0.18 X 10(7) M-1). The mean Ka value for the five subjects with FAP of the Appalachian type was slightly but not significantly reduced (1.08 +/- 0.11 X 10(7) M-1). There was no overlap of individual Ka values of subjects with types I and II TBPA with those of subjects from all other groups. Abnormalities of thyroid function included slight but significant reductions of the mean total serum T4 concentration in the subjects with type II FAP and the mean serum total T3 concentration in those with type I FAP. Four subjects with FAP (two type II and two of the Appalachian type) had biochemical evidence of hypothyroidism. The three subjects with total serum T3 levels below the limit of normal had amyloid cardiomyopathy. These results indicate that TBPAs from subjects with FAP types I and II have relatively lower affinity for T4. Although none of the substituted amino acids in these variant TBPAs contribute directly to the surface of the putative T4-binding site, the side chains of amino acids 30 and 84, but not 60, interact with internal residues of the beta-structure which forms the presumed binding site, in agreement with our results of Ka measurements. The high incidence of hypothyroidism is due to the probably fortuitous occurrence of Hashimoto's thyroiditis as well as to partial destruction of the thyroid gland by amyloid deposits.

Amyloidosis↗
PubMed1978

An IgG2a-producing variant of an IgG2b-producing mouse myeloma cell line. Structural studies on the Fc region of parent and variant heavy chains.

The IgG2b-producing MPC 11 mouse myeloma cell line has yielded a number of variants which synthesize heavy chains characteristic of a different immunoglobulin subclass, IgG2a, as previously shown by serology, peptide maps, and assembly profiles. We have studied the Fc regions of the IgG2a protein synthesized by one variant, ICR 9.9.2.1, and of the IgG2b protein synthesized by MPC 11 and compared them to MOPC 173, an IgG2a protein of known sequence. We analyzed the Fc regions of the three immunoglobulins by several analytical techniques, such as immunoelectrophoresis of papain digests, NaDodSo4-polyacrylamide gel electrophoresis analyses of Fc CNBr fragments, and comparative ion-exchange chromatography of radiolabeled tryptic and chymotryptic Fc peptides. In addition, Fc CNBr fragments of the variant gamma2a and MPC 11 gamma2b molecules were isolated and subjected to amino acid analysis and partial sequence determination. From these data, we concluded that the Fc fragment of ICR 9.9.2.1 is most probably identical to that of MOPC 173 and different from the parental gamma2b Fc fragment. A number of residue positions which discriminate between gamma2b and gamma2a sequences are described. In two of three segments sequenced, gamma2b and gamma2a molecules share more identical residues than either shares with another mouse subclass, gamma1.

Amino Acid Sequence↗
PubMed1997

Structural characterization of four genetic variants of human serum albumin associated with alloalbuminemia in Italy.

A long-term electrophoretic survey on plasma proteins, which was carried out in several clinical laboratories in Italy, identified 28 different genetic variants of human serum albumin and four cases of analbuminemia. We have previously characterized 16 point mutations, 3 C-terminal mutants, and the genetic defects in two analbuminemic subjects. Here, we report the molecular defects of four alloalbumins that have been characterized by protein structural analysis. Of these, three represent new single-point mutations: albumins Tregasio, Val122-->Glu, Bergamo, Asp314-->Gly, and Maddaloni, Val533-->Met. The fourth, albumin Besana Brianza, has the same Asp494-->Asn mutation that introduces a glycosylation site which has been previously reported in a variant from New Zealand, albumin Casebrook. However, in contrast to albumin Casebrook, albumin Besana Brianza is only partially glycosylated and the oligosaccharide is heterogeneous, consisting of a biantennary complex type N-glycan with either two or one sialic acid residue(s) on the antennae. Both albumin Maddaloni and Besana Brianza represent mutations at hypermutable CpG dinucleotide sites; albumin Maddaloni is a mutant that does not involve a charged amino acid.

Amino Acid Sequence↗
PubMed1980

Immunological and structural relatedness of isozymes and genetic variants of 3-phosphoglycerate kinase from the mouse.

Isozymes (PGK-1 and PGK-2) and genetic variants (PGK-2A, PGK-2B, and PGK-2C) of 3-phosphoglycerate kinase were purified by affinity chromatography using an 8-(6-aminohexyl)-amino-ATP-Sepharose column as the key step. Antisera raised against purified PGK-1 and PGK-2A were tested for specificity and cross-reactivity by application of double immunodiffusion and enzyme immunoinactivation methods. By double immunodiffusion, no precipitin lines were observed between anti-PGK-2A and PGK-1, but a weak cross-reactivity between anti-PGK-1 and PGK-2A was detected. In addition to specific inhibition of PGK-1 and PGK-2A by their respective antisera, anti-PGK-1 was shown to inhibit PGK-2 activity at high antiserum concentrations, whereas no inhibition of PGK-1 activity by anti-PGK-2A was observed. The amino acid compositions of PGK-1 and PGK-2 revealed a certain degree of homology. However, tryptic peptide maps showed no obvious similarity in the peptide spots between these two 3-phosphoglycerate kinase isozymes. Three electrophoretic variants of PGK-2 were compared biochemically and immunologically. PGK-2C from C57L/J mice, a low activity variant, was shown to be the result of a structural gene mutation that affects the active site of the enzyme.

Amino Acids↗
PubMed1994

The disulfide bridges of toxin 2 from the scorpion Centruroides noxius Hoffmann and its three-dimensional structure calculated using the coordinates of variant 3 from Centruroides sculpturatus.

The disulfide bridges of toxin 2 from the venom of the scorpion Centruroides noxius Hoffmann were found by amino acid sequence determination of fragments of native toxin, produced by enzymatic cleavage and separated by high-performance liquid chromatography (HPLC). They are: Cys12-Cys65, Cys16-Cys41, Cys25-Cys46 and Cys29-Cys48. The coordinates of the X-ray diffraction structure of toxin variant 3 of C. sculpturatus [(1980) Proc. Natl. Acad. Sci. USA 77, 6496-6500] were used to construct a three-dimensional model of toxin 2. All the amino acid replacements were easily accommodated, and the modeled structure reveals a clustered pattern of sequence variation, which may help to identify residues responsible for functional differences among toxins of mammals and insects.

Amino Acid Sequence↗
PubMed1999

New p73 variants with altered C-terminal structures have varied transcriptional activities.

p73 has been identified as a protein which shares significant homology with the tumor suppressor p53. We found two new types of splicing variant mRNAs for p73 expressed in MCF-7 cells which we named p73gamma and epsilon. Sequence analysis revealed that these mRNAs encode variant p73 proteins bearing distinct carboxy-terminal structures, which are also different from the previously reported variants p73alpha and beta. The mRNAs encoding p73gamma and epsilon as well as alpha and beta were confirmed to be expressed in normal human tissues in varied patterns. All of these splicing variants activated promoter with the p53-binding consensus sequence, but to different degrees. Furthermore, suppressive effects of p73alpha, gamma and epsilon, but not beta, on endogenous p53 activity were observed when transiently expressed in HepG2 and MCF-7 cells. These results suggested that the carboxy-terminal regions of p73 which were altered by alternative splicing affect these transactivation abilities and modulate the functions of p73 molecules.

Alternative Splicing↗
PubMed1990

Primary structures of two protamine 2 variants (St2a and St2b) from stallion spermatozoa.

Protamines were extracted from stallion sperm cell nuclei, alkylated with iodoacetamide and separated by reversed-phase high-performance liquid chromatography. Two main components, protamine 1 and protamine 2, were obtained. The latter contains two subspecies, separable by acetic acid-urea-polyacrylamide gel electrophoresis. The primary structure of protamine 2a (St2a) was determined by analysis of fragments obtained from purified protamine 2 peak by thermolysin digestion. The digested peptides were separated by acetic acid-urea gel electrophoresis and, after electroblotting onto a polyvinylidene difluoride filter, their amino acid sequences were determined by pulse liquid peptide sequencing. The amino acid sequence of protamine 2b was predicted from the double sequence data of protamine 2 peak by eliminating the amino acid of St2a in each cycle. St2a and St2b were found to contain 62 and 58 amino acid residues, respectively, and they seem to be homologous with type 2 protamines from human and mouse spermatozoa.

Alkylation↗