Biomedical subjects

H W Jarrett

Publications and source records attributed to H W Jarrett.

At least 37 records · Page 2Linked to original sources

PubMed1996

Ca2+-calmodulin binds to the carboxyl-terminal domain of dystrophin.

The unique COOH-terminal domain of dystrophin (mouse dystrophin protein sequences 3266-3678) was expressed as a chimeric fusion protein (with the maltose-binding protein), and its binding to calmodulin was assessed. This fusion protein, called DysS9, bound to calmodulin-Sepharose, bound biotinylated calmodulin, caused characteristic changes in the fluorescence emission spectrum of dansyl-calmodulin, and had an apparent affinity for dansyl-calmodulin of 54 nM. Binding in each case was Ca2+-dependent. The maltose-binding protein does not bind calmodulin, and thus binding resides in the dystrophin-derived sequences. Deletion mutation experiments further localize the high affinity calmodulin binding to mouse dystrophin protein sequences 3293-3349, and this domain contains regions with chemical characteristics found in the calmodulin-binding sequences in other proteins. The COOH-terminal domain provides sites of attachment of dystrophin to membrane proteins, and calmodulin binding may modulate these interactions.

Amino Acid Sequence↗

PubMed1995

Interactions between dystrophin glycoprotein complex proteins.

The organization of the dystrophin glycoprotein complex (DGC) was studied by investigating interactions between its components. For this purpose, mouse dystrophin and syntrophin-1 (alpha-syntrophin) sequences were expressed as chimeric fusion proteins and used in overlay binding experiments to probe gel blots of purified rabbit muscle DGC. In order to identify the DGC proteins that bind to different regions of dystrophin, the amino-terminal 385 amino acids, the unique carboxy-terminal domain (amino acids 3266-3678), and the adjacent cysteine-rich region of dystrophin homologous to alpha-actinin (amino acids 3074-3265) were expressed as separate fusion proteins. The cysteine-rich sequences of dystrophin predominantly bound adhalin (gp50) and to full length dystrophin suggesting that these sequences may also be important to dystrophin dimerization. The carboxy-terminal domain sequences strongly bound all of the DGC syntrophins and weakly, adhalin, while the amino-terminal sequences of dystrophin bound none of the proteins of this complex. Fusion proteins containing alpha-syntrophin sequences bound not only to dystrophin but also to all three DGC syntrophins, adhalin, and gp35. The interactions identified here were used to refine the existing model of DGC organization to make it consistent with the current data.

Animals↗

PubMed1995

Preparation of cDNA-silica using reverse transcriptase and its DNA sequence determination.

A new method for producing macroporous silica (suitable for high-performance liquid chromatography) with covalently attached DNA is presented. The method uses (dT)18-silica as a primer, annealed to a poly(A)-RNA template, which is then transcribed using reverse transcriptase. The RNA template is eluted and single-stranded cDNA-silica is recovered. The cDNA-silica can be sequenced using the dideoxy method. These methods provide a facile method for producing cDNA-silica of demonstrable authenticity and provide a unique approach to DNA and RNA sequencing.

Base Sequence↗

PubMed1995

Alternate binding of actin and calmodulin to multiple sites on dystrophin.

Mouse dystrophin protein sequence 1-385 and various deletion mutants were expressed in Escherichia coli as fusion proteins, and the binding of actin, calmodulin, and troponin C were characterized. The fusion protein-containing sequence 1-385 bound actin with an apparent dissociation constant of 129 +/- 65 nM as measured using a solid-phase immunoassay. High affinity was also observed with ultracentrifuge cosedimentation assays and biotinylated-actin binding assays. Results with deletion mutants and analysis based upon sequence homology were consistent with two or three high affinity F-actin-binding sequences within this region of dystrophin at sequence positions 18-37 (ABS 1), 128-149 (ABS 2), and potentially at a new region called ABS 3 (86-120). A fusion protein lacking these sequences but containing dystrophin triple-helix sequences also bound actin but with reduced affinity. Calmodulin binds to dystrophin sequence 1-385 in a Ca(2+)-dependent manner and competitively inhibits F-actin binding. Results were consistent with two Ca(2+)-calmodulin-binding sites in this region of dystrophin at approximate sequence positions 18-42 (CBS 1) and 104-125 (CBS 2) with calmodulin affinities of 2.1 +/- 1 and 1.6 +/- 1.2 microM, respectively. Troponin C can substitute for calmodulin, although it binds with about 2-fold lower affinity. These results suggest that calmodulin (or troponin C) binding alternates with and may regulate F-actin binding by dystrophin much as has been postulated for other cytoskeletal proteins which are homologous to dystrophin.

Actins↗

PubMed1994

Novel DNA-Sepharose purification of the FadR transcription factor.

A DNA sequence bound by the FadR transcription factor of Escherichia coli was covalently attached to Sepharose by two different approaches: by chemical coupling or by template-directed enzymatic synthesis using a DNA polymerase. The two kinds of DNA-Sepharose were packed into small columns and used for the purification of the FadR protein; chromatography was without using competitor DNA and the supports contained single-copy, non-repetitive DNA sequences. Comparison showed that the enzymatically prepared support, while having less bound DNA, bound more FadR protein than did the chemically prepared support. This probably results from the lack of detrimental DNA modification by the gentle enzymatic procedure. The chemically prepared support was of lower capacity but yielded purer FadR protein when compared under the same elution conditions. This may be explained by the simpler DNA sequence which could be coupled chemically; less contaminating proteins were bound by the simpler DNA sequence. However, the enzymatically prepared support could also yield comparable purity if the protocol was modified to include additional washes with salt containing buffers. In all cases, FadR was eluted from the DNA using high-salt (0.8 M) mobile phase; ligand-specific elution of FadR using a fatty acyl-coenzyme A thiol ester was ineffective. Affinity chromatography on DNA-Sepharose provided a more rapid, simple purification of FadR than conventional purification techniques and yielded biologically active protein.

Bacterial Proteins↗

PubMed1994

Calmodulin-activated phosphorylation of dystrophin.

Purified dystrophin glycoprotein complex (DGC) contains an endogenous protein kinase activity which phosphorylates dystrophin. Mg2+ (or Mn2+) and ATP are required for this phosphorylation. Ca(2+)-calmodulin increases the rate of phosphorylation of dystrophin 12-fold relative to the EGTA control, while other protein kinase activators, cAMP and cGMP, have no effect. Phosphorylation of other proteins in the DGC preparation was observed, with a 59-kDa protein also being phosphorylated in a calmodulin-dependent manner. These phosphorylations were all on serine residues. The DGC protein kinase activity also phosphorylates syntide-2, a peptide substrate for CaM kinase II, and antibodies raised against CaM kinase II cross-react with DGC blotted onto nitrocellulose. Further, purified, baculovirus-expressed CaM kinase II phosphorylates dystrophin and also phosphorylates at least one of the peptides of dystrophin which is phosphorylated by the DGC protein kinase activity, as shown by tryptic peptide maps. CaM kinase II also phosphorylates other proteins present in the DGC preparation that are phosphorylated by the endogenous protein kinase. Finally, dystrophin sequence 2618-3074, produced by recombinant techniques, is phosphorylated by both the DGC protein kinase and purified CaM kinase II. Since dystrophin and two other DGC components have also been shown to bind calmodulin, two important components of signal transduction--calmodulin binding and protein phosphorylation--operate in the DGC.

Animals↗

PubMed1993

The model calmodulin-binding peptide melittin inhibits phosphorylase kinase by interacting with its catalytic center.

The inhibition by melittin, a model calmodulin-binding peptide, of phosphorylase kinase, which contains an intrinsic calmodulin subunit, has been characterized in detail. The inhibition was competitive with respect to phosphorylase b for both the phosphorylase kinase holoenzyme and its isolated catalytic gamma-subunit (minus calmodulin), and the ratios of the Km for phosphorylase to the Ki for melittin were similar for both forms of the kinase. These findings indicate that inhibition of the phosphorylase kinase holoenzyme by melittin is caused predominantly by its interaction with the catalytic subunit of the enzyme, and not with the endogenous calmodulin subunit. Further proof that melittin interacts directly with the catalytic site was obtained when it was observed that melittin was also a substrate for phosphorylase kinase, with a Km that was less than that for phosphorylase b, although the kcat/Km specificity constant was only 1/200th of that for phosphorylase. The apparent tight binding of melittin to the kinase active site could not be readily rationalized by conventional comparison of sequence similarity between melittin and phosphorylase; however, considerable sequence similarity, centered around the convertible seryl residue of phosphorylase, was observed when the sequences were aligned in reversed polarity. The possible regulatory significance of the direct interaction of the catalytic site of this Ca(2+)-dependent kinase with a calmodulin-binding peptide is discussed.

Amino Acid Sequence↗

PubMed1993

Chromatographic stability of glucose-silica.

Glucose-silica was prepared and packed into five 100 x 4.6 mm I.D. columns. These columns were tested initially with selected protein mixtures. Each of the columns was stored in one combination of buffer (100 mM sodium sulfate, 20 mM sodium phosphate, pH 6.8), temperature (4 or 20 degrees C), methanol and sodium azide. After a year, we found that storing glucose-silica columns in the buffer containing sodium azide or methanol at 4 degrees C was necessary to prolong stability in storage. However, glucose-silica also exhibited some dynamic instability.

Chromatography, Gel↗

PubMed1993

Affinity chromatography with nucleic acid polymers.

Column chromatography utilizing polynucleotides immobilized on solid support is reviewed. This form of affinity chromatography is used for the isolation of polynucleotides and polynucleotide binding proteins, and to a lesser extent for analysis. Several specific applications within these categories have been widely used in the biomedical sciences. Poly(A) mRNA is routinely isolated using oligo(dT) or oligo(dU) supports. Many DNA binding proteins, including transcription factors, restriction endonucleases, and proteins involved in DNA repair, replication, recombination, and transposition have been purified using DNA affinity chromatography. Recently, DNA supports suitable for use in high-performance liquid chromatography have been described and utilized. The current usage of DNA affinity chromatography is reviewed and potential future uses for this technology are speculated upon.

Animals↗

PubMed1993

Activation of enzymes by calmodulins containing intramolecular cross-links.

We have reacted calmodulins containing cysteines substituted at positions 3 and 146 or 5 and 146 with bismaleimidohexane (BMH) to generate intramolecularly cross-linked proteins termed BMHCM or BMHCM1, respectively. Reactions were also performed with N-ethylmaleimide (NEM) in place of BMH to generate corresponding S-ethylsuccinimidylated proteins termed NEMCM or NEMCM1. The abilities of these proteins to activate plant NAD kinase, erythrocyte Ca(2+)-ATPase and bovine brain calcineurin activities were assessed. The BMH- or NEM-reacted proteins activate calcineurin activity as does control calmodulin. Kact values for Ca(2+)-ATPase activation by BMHCM and BMHCM1 are increased 10-fold relative to the control value, with no corresponding change in Vmax values. Activation of this enzyme by NEMCM or NEMCM1 is not different from the control. In NAD kinase activation experiments BMHCM and BMHCM1 are associated with a 10 to 20-fold increase in Kact values and a 60-75% reduction in Vmax values relative to the control. NEMCM1 is not associated with any apparent changes in NAD kinase activation, however, NEMCM is associated with a 10-fold increase in the Kact value. NEM-reacted calmodulin containing a cysteine only at position 3 is not associated with an increased Kact value, implying that this change is due to interactions between S-(ethylsuccinimido)cysteines at positions 3 and 146. In conclusion, cross-linking and associated distortions in the structure of calmodulin appear to have little or no effect on activation of calcineurin enzyme activity. However, bending in the central helix and/or steric restrictions associated with cross-linking increase significantly the Kact value for Ca(2+)-ATPase and NAD kinase activation, and dramatically reduce maximal activation of NAD kinase activity.

Brain↗

PubMed1992

Calmodulin specifically binds three proteins of the dystrophin-glycoprotein complex.

Dystrophin is the approximately 400,000 Da. protein (p400K) product of the Duchenne muscular dystrophy gene locus. In the sarcolemma membrane, it is associated with several other proteins, many of which are glycoproteins (abbreviated gp) and include gp156K, p59K, gp50K, gp43K, gp35K, and p25K. Here, we show that dystrophin, gp156K, and p59K are calmodulin-binding proteins, the binding is Ca(2+)-dependent, and of high-affinity similar to that seen with calmodulin-activated enzymes. Two putative calmodulin-binding sequences were identified, one at either end of the dystrophin sequence.

Animals↗

PubMed1992

High-performance affinity chromatography of DNA. II. Porosity effects.

A DNA-silica, (dT)18-silica, was prepared and used in a study of the chromatography of the oligonucleotide, (dA)18, based upon base pairing. It was shown that hybridization efficiency did not depend upon flow-rates up to 2 ml/min for the small columns (22 x 2 mm) used. As increasing amounts of (dA)18 were loaded onto the columns, the columns were found to saturate at a well defined capacity that was always less than the amount that theoretically could have been bound. Maximum capacity was achieved whenever the loading temperature was at least 20-25 degrees C below the temperature at which the loaded oligonucleotide would elute. The effects of porosity on both coupling efficiency and capacity were measured and suggest that pore sizes in the 300-500 A range are most appropriate for this form of chromatography.

Chromatography, Affinity↗

PubMed1992

Enzymatic syntheses of DNA-silicas using DNA polymerase.

Oligothymidylic acids couple to an activated ester silica (N-hydroxysuccinimidyl-silica) only when they contain an added aminoalkyl group. Heteropolymeric oligomers containing other nucleotide bases were shown to also couple by way of the nucleotide base (adenine, cytosine, or guanine); however, when a heteropolymeric oligonucleotide also contains a 5'-aminoalkyl moiety, coupling by way of the latter is the favored reaction. When duplex hybrids of oligonucleotides are formed, the nucleotide bases are protected from chemical coupling. Coupling by way of nucleotide bases would be detrimental to some chromatography experiments. On the basis of these observations, two different procedures were developed to produce DNA-silicas in which a single strand of the DNA is coupled by only its 5'-terminus. In the first of these, the polymerase chain reaction was used with a 5'-aminoalkyl primer to make a duplex DNA with one strand containing the 5'-aminoalkyl group and the duplex DNA is then coupled to the activated ester silica. This yielded a silica containing about 0.17 nmol of a 242-mer per gram silica which bound only probes specific for the coupled strand. In the other procedure, a template DNA strand was poly(A) tailed and hybridized to (dT)18-silica. DNA polymerase I (Klenow large fragments) was then used to copy the template-specified sequence directly onto the 3'-terminus of the (dT)18. This procedure yielded about 1.2 to 2.7 nmol DNA copied/g of silica of a specific 21-mer sequence. The DNA-silica produced selectively hybridized only with complementary sequences and not with DNA lacking that sequence. Either of these procedures thus produces DNA-silicas from heteropolymeric DNA sequences with a predetermined, specific 5'-terminal site of attachment.

Base Sequence↗

PubMed1991

High-performance affinity chromatography of messenger RNA.

A 50-mer of thymidylic acid, (dT)50, was coupled to silica inside prepacked columns using the N-hydroxysuccinimide chemistry. The resulting (dT)50-silica columns were used to resolve oligomers of adenylic acid, (dA)19-24, and to separate poly(A) mRNA (messenger RNA) from Saccharomyces. Oligomers which differed in length by a single nucleotide base were readily resolved. Using either (dT)50- or (dT)18-silica, poly(A) mRNA could be purified in as little as 8 min. The poly(A) mRNA isolated appeared to be full length and could be used directly for T4 RNA ligase and RNAse A and T1 enzymatic reactions. The (dT)50-silica column was used to fractionate total poly(A) mRNA by tail length. While the separation was primarily due to poly(A) tail length, most fractions appeared to contain multiple tail lengths. Whether this represents an intrinsic feature of the RNA or a limitation of the method is discussed. These studies show that polynucleotides in the kilobase size range can be separated rapidly and with good resolution on DNA-silica.

Chemical Precipitation↗

PubMed1991

Trifluoperazine binding to mutant calmodulins.

Trifluoperazine (TFP) binding by 14 calmodulins, including 12 produced by site-directed mutagenesis, was determined. While vertebrate calmodulin binds 4.2 +/- 0.2 equiv of TFP, Escherichia coli expressed but unmutated calmodulins bind about 5.0 +/- 0.5 equiv of TFP. The cause for this difference is not known. The E. coli expressed proteins consist of two different series expressed from different calmodulin genes, CaMI and SYNCAM. The wild-type genes code for proteins that differ by nine conservative amino acid substitutions. Both these calmodulins bind 5 equiv of TFP with similar affinities, thus none of these conservative substitutions has any additional effect on TFP binding. Some altered calmodulins (deletion of EE83-84 or SEEE81-84, changing DEE118-120----KKK, M124----I,E120----K, or E82----K) have no appreciable effect on TFP binding. Other mutations affect either the binding of one TFP (deletion of E84) or about two TFP (changing E84----K, EEE82-84----KKK, E67----A, DEQ6-8----KKK, or E11----K). The mutations that affect TFP binding are localized to three regions of calmodulin: The amino-terminal alpha-helix, the central helix between the two globular ends of calmodulin, and a calcium-binding site in the second calcium-binding domain. The results are consistent with each of these regions either directly participating in drug binding or involved structurally in maintaining or inducing the correct conformation for TFP binding in the amino-terminal half of calmodulin.

Amino Acid Sequence↗

PubMed1991

Calmodulin-binding proteins also have a calmodulin-like binding site within their structure. The flip-flop model.

The flip-flop model is a mechanistic model proposed to describe how calmodulin activates enzymes. One prediction based upon this model is that calmodulin-activated enzymes would contain a calmodulin-like binding site which, among other attributes, would bind the peptide melittin. Five purified calmodulin-activated enzymes, namely calcineurin, myosin light chain kinase, phosphorylase b kinase, phosphodiesterase, and NAD kinase, were all found to bind biotinylated melittin and to also bind an antimelittin antibody and biotinylated calmodulins. Using gel blots of crude tissue extracts (rat brain and Arabidopsis), most proteins did not bind any of the probes and thus do not have these characteristics. However, among those which bind any of these probes, a strong correlation was found between those proteins which bind biotinylated calmodulins and those which bind melittin and antimelittin. Gel blots of phosphorylase b kinase demonstrate that the alpha, beta, and gamma subunits all bind calmodulin and melittin. A putative calmodulin-like binding site sequence was identified in eight enzymes or subunits which may play an important role in both melittin binding and calmodulin-dependent regulation of these enzymes.

Amino Acid Sequence↗

PubMed1991

Cloning and disruption of the yeast C-8 sterol isomerase gene.

The yeast ERG2 gene codes for the C-8 sterol isomerase, an enzyme required for the isomerization of the delta 8 double bond to the delta 7 position in ergosterol biosynthesis. The ERG2 gene was cloned by complementation of a C-8 sterol isomerase mutant strain (erg2). The complementing region of DNA required to restore ergosterol synthesis to erg2 was limited to a 1.0 kb StuI-BglII fragment. In order to determine whether the ERG2 gene was essential for yeast viability, a LEU2 gene was inserted into the NdeI site (made blunt) of this 1.0 kb fragment. Transformation of a wild type diploid strain with the ERG2 substituted DNA resulted in the generation of viable haploids containing the erg2 null allele (erg2-4::Leu2). These results suggest that the C-8 sterol isomerase activity is not essential for yeast cell viability. This disruption represents the second ergosterol biosynthetic gene in the distal portion of the pathway to be disrupted without adversely affecting cell viability.

Cloning, Molecular↗

PubMed1990

Glucose-silica, an improved medium for high-pressure gel filtration chromatography.

Glucose was covalently coupled to aminopropyl derivatized silica of various pore sizes. The reaction most likely involved Schiff's base formation between the aldehyde of glucose and the amine on the silica which was then reduced with NaCNBH3. This glucose-silica behaved as a nearly ideal molecular sieving support for the high-pressure gel filtration chromatography of proteins and was superior in performance to many currently available supports.

Calmodulin↗