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M Schiffer

Publications and source records attributed to M Schiffer.

At least 91 records · Page 5Linked to original sources
PubMed1988

Dual conformations of an immunoglobulin light-chain dimer: heterogeneity of antigen specificity and idiotope profile may result from multiple variable-domain interaction mechanisms.

The structure of an immunoglobulin antigen-binding fragment (Fab) has been thought to be invariantly defined by well-conserved amino acid residues in the variable domains of the heavy and light chains. These conserved residues enable folding of the polypeptide segments into the characteristic immunoglobulin fold domains and are the major controllers of interactions between domains. However, crystallographic studies of some immunoglobulin light-chain dimers have suggested and the crystallographic structure of the Fab in an Fab-neuraminidase complex may have proven that antibodies are not restricted to a single, invariant relative positioning of the two variable domains. We propose that in some cases the detailed quaternary structural relationships between the variable domains of heavy and light chains are not restricted to those of the canonical Fab. It is unclear whether alterations of these relationships occur only after complex formation with antigen or, if in ligand-free solution, Fab conformers might coexist in relative concentrations determined by isomerization rates. In the latter case, antibody-presenting lymphocytes may be polyspecific, and the specificity of lymphocytes might be modulated by anti-idiotopic antibodies complexed to cell surface receptors. In either case, the idiotopic repertoire displayed by an antibody or lymphocyte surface receptor might be changed by the presence or absence of antigen.

Antibody Diversity↗
PubMed1986

Relationships between liquid- and solid-phase antibody association characteristics: implications for the use of competitive ELISA techniques to map the spatial location of idiotopes.

A liquid-phase assay system based on small-zone size-exclusion chromatography was used to examine the binding of a monoclonal anti-idiotopic antibody, F6, to its idiotope on the murine plasmacytoma IgA, TEPC-15. Chromatographic behavior revealed a strong association between T-15 and F6, which was previously characterized by solid-phase immunoassay as recognizing a nonbinding site epitope of the T-15. This chromatographic pattern suggests that the inability of the hapten phosphorylcholine to inhibit the anti-idiotope:idiotope relationship in solid-phase immunoassay might be equally explained by the low affinity of the hapten relative to the high affinity of the anti-idiotope antibody. Bivalent interactions between solid-phase IgA and liquid-phase IgG should enhance the binding of the anti-idiotope to an extent that would prevent the hapten from dissociating the complex. Under these solid-phase assay conditions, observation of hapten inhibition may, in some cases, indicate site specificity, but absence of inhibition cannot be interpreted. Computer simulations of solid-phase hapten inhibition scenarios were used to evaluate the qualitative nature of binding inhibition profiles expected under various conditions of liquid- and solid-phase reactant affinities and concentrations. The apparently unusual inhibition curves previously observed in the T-15:anti-T-15 studies in which the degree of binding inhibition by hapten appeared to be independent of anti-idiotope concentration may be predictable in cases of excess solid-phase epitope; the plateau inhibition value is a function of relative affinity constants and concentrations of solid-phase and inhibitor components. The results additionally suggest that the affinity of a liquid-phase antibody may modulate the effective concentration of solid-phase epitope.

Antibody Affinity↗
PubMed1986

Structure of Rhodopseudomonas sphaeroides R-26 reaction center.

The molecular replacement method has been successfully used to provide a structure for the photosynthetic reaction center of Rhodopseudomonas sphaeroides at 3.7 A resolution. Atomic coordinates derived from the R. viridis reaction center were used in the search structure. The crystallographic R-factor is 0.39 for reflections between 8 and 3.7 A. Validity of the resulting model is further suggested by the visualization of amino acid side chains not included in the R. viridis search structure, and by the arrangements of the reaction centers in the unit cell. In the initial calculations quinones or pigments were not included; nevertheless, in the resulting electron density map, electron density for both quinones QA and QB appears along with the bacteriochlorophylls and bacteriopheophytins. Kinetic analysis of the charge recombination shows that the secondary quinone is fully functional in the R. sphaeroides crystal.

Bacterial Proteins↗
PubMed1986

Subgroups of variable region genes of beta chains of T-cell receptors for antigen.

The beta-chain variable regions of 6 human, 21 mouse, and 1 rabbit T-cell receptors for antigen, including two pairs of duplicates, have been classified into two subgroups. Subgroup I has an invariant Phe at residue 65 and a salt bridge can be formed between the Asp at position 86 and the 11 Arg, 2 Lys, and 1 His residues at position 64. In one instance Tyr replaces Asp at position 86 so that a salt bridge cannot be formed with the Lys at position 64. Subgroup II has an invariant Tyr at residue 65; 8 chains have Gly and 3 have Ala at position 63. These 3 have Asp at position 64. Those with Gly-63 cannot form a salt bridge in this region of the beta chain. The 3 with Asp-64 have Arg at position 86, can form a reverse salt bridge, and could constitute a third subgroup. The relation of these findings to functional parameters in beta chains of the T-cell receptors for antigen deserves further study. The use of variability plots on the assumption that the beta chains are a single population may be misleading for the variable region. Most of the variability in the expressed beta chains would be created by variable-diversity-joining assortment, junctional diversity, and the possible insertion of N sequences.

Amino Acid Sequence↗
PubMed1985

Formation of an infinite beta-sheet arrangement dominates the crystallization behavior of lambda-type antibody light chains.

The packing interactions in crystals of human lambda-type antibody light chain dimers have been reviewed. These homologous proteins are composed of individually specific variable domains, but all have very similar constant domain sequences. The proteins do not emulate each other in their overall crystallization behavior: each attains an individually characteristic space group or unit cell dimensions. However, each of these protein crystals has one unit cell dimension in common, 72.4(+/- 0.2) A. Examination of the protein packing in these crystals reveals that the common cell dimension is a consequence of a packing arrangement of their constant domains, which is conserved in all three crystals. In this striking arrangement, beta-sheets of adjacent constant domains are placed in juxta-position to form an "infinite chain". Although this constant domain packing pattern is rigorously conserved, the variable domain packing arrangements in each of these crystals are different. The conservation of the "infinite" beta-sheet pattern suggests that the constant domain interactions dominate the thermodynamic energy of lattice formation, probably through a combination of specific hydrogen bond formations and by a decrease in the solvent-accessible surface. A single amino acid substitution prohibits this characteristic interneighbor hydrogen bond pattern in the homologous kappa-type light chains. This may explain the observation that very few kappa-type light chains have been crystallized.

Crystallography↗
PubMed1985

Characterization of bacterial photosynthetic reaction center crystals from Rhodopseudomonas sphaeroides R-26 by X-ray diffraction.

An orthorhombic crystal form (P2(1)2(1)2(1)) of the reaction center from the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26 has been characterized. The crystals were grown from polyethylene glycol; the unit cell dimensions are a = 142.2 A, b = 139.6 A, and c = 78.7 A; and they contain one reaction center in each crystallographic asymmetric unit. The crystals diffract to at least 3.0 A resolution, and are suitable for detailed structural studies.

Bacterial Proteins↗
PubMed1985

Novel arrangement of immunoglobulin variable domains: X-ray crystallographic analysis of the lambda-chain dimer Bence-Jones protein Loc.

We have characterized and crystallized a human lambda I light-chain dimer, Bence-Jones protein Loc, which has variable (V) region antigenic determinants characteristic for the lambda I subgroup and constant (C) region determinants of the C lambda I gene Mcg. The crystal structure was determined to 3-A resolution; the R factor is 0.27. The angle formed by the twofold axes of the V and C domains, the "elbow bend", is 97 degrees, the smallest found so far for an antibody fragment. The antigen-binding site formed by the two V domains of the Loc light chain differs significantly from those of other immunoglobulin molecules (light-chain dimers and Fab fragments) for which X-ray crystallographic data are available. Whereas, in other antibody fragments, the V domains are related by a local twofold axis, a local twofold screw axis with a translational component of 3.5 A relates the V domains in protein Loc. In contrast to the classic antigen binding "pocket" formed by V domain interactions in the previously characterized antibody structures, the V region associations in protein Loc result in a central protrusion in the binding site, with grooves on two sides of the protrusion. The structure of protein Loc indicates that immunoglobulins are physically capable of forming a more diverse spectrum of antigen-binding sites than has been heretofore apparent. Moreover, the unusual protruding nature of the binding site may be analogous to structures required for some anti-idiotypic antibodies. Further, the complementarity-determining residues form parts of two independent grooves.(ABSTRACT TRUNCATED AT 250 WORDS)

Bence Jones Protein↗
PubMed1985

Normal excretory urography in patients with primary kidney neoplasms.

The records of 65 consecutive patients discharged from the hospital with a diagnosis of primary parenchymal neoplasm of the kidney were reviewed. Four of the 65 patients had neoplasms which were not detected by excretory urography. The 4 undetected lesions included 3 renal cell carcinomas and 1 oncocytoma. All of these lesions projected from the anterior or posterior surface of the kidney, and all 4 were clearly demonstrated by computed tomography. Normal findings on an excretory urogram do not completely exclude a neoplasm of the kidney. When there is strong clinical suspicion of a renal neoplasm, computed tomography should be the initial examination or should be done even if the urogram has shown normal findings.

Adenoma↗
PubMed1984

Significance of cone biopsy margins in the management of patients with cervical neoplasia.

Too many patients in the United States undergo hysterectomy for cervical neoplasia following cone biopsy because too many gynecologists choose not to pay attention to the pathology present at the margins of the cone specimen. In view of the need to improve the management of cervical neoplasia--i.e., to reduce the number of needless hysterectomies--a retrospective study was done to verify the trend in our institution and to evaluate the utilization of cone biopsy to determine the extent of the process. Also, the methods used for procuring the cone sample and for interpreting the results of the biopsy were studied. The present study included 345 patients who underwent a cone biopsy; subsequently, 102 of them had a hysterectomy. Based on the evaluation of the cases in this study, information was obtained about the performance of cone biopsy and the guidelines for determining when a hysterectomy should be performed and when other, less drastic means of eradicating the neoplasia should be considered.

Adult↗
PubMed1982

Small-angle neutron scattering study of Bence-Jones protein Mcg: comparison of structures in solution and in crystal.

Immunoglobulins fragments are composed of globular domains linked by extended polypeptide segments. The molecular flexibility inherent in this arrangement allows for significant potential differences between structures observed in the crystalline state and those attained in solution. Small-angle neutron scattering measurements in dilute solution were performed on the Mcg Bence-Jones protein dimer, for which performed on the Mcg Bence-Jones protein dimer, for which accurate atomic coordinates have been determined by crystallographic methods [Edmundson, A. B., Ely, K. R., Abola, E. E., Schiffer, M., & Panagiotopoulos, N. (1975) Biochemistry 14, 3953-3961; Schiffer, M. (1980) Biophys. J. 32, 230-232]. The measured radius of gyration (Rg) in H2O buffer is 24.0 +/- 0.4 A and in D2O buffer is 23.3 +/- 0.1 A; the calculated value of Rv (Rg in vacuo) is 24.0 A. The above values compare well with the calculated Rg value of 23.6 A when refined coordinates of the trigonal crystal form of the Mcg Bence-Jones protein are used. On the basis of a match point of 44.2% D2O concentration, the experimental partial specific volume is 0.74 cm3/g. The experimentally derived molecular weight of 47 000 is in very good agreement with that (45 500) calculated from the amino acid composition. For comparison with different Fab's (antigen binding fragments) exhibiting various "elbow bends" due to the flexibility of the switch peptide between variable and constant domains of the immunoglobulin chains, calculation of the Rg value of the Mcg dimer was performed as a function of the elbow bend. The Rg varied from 22.8 to 26.0 A as the elbow bend was opened from 100 degrees to 180 degrees; the maximum radius of gyration of the particle was 26.5 A with the switch peptide stretched by separating the variable and constant domains by an additional 1.5 A at an elbow bend of 180 degrees.

Bence Jones Protein↗
PubMed1981

Computer simulation of protein self-association during small-zone gel filtration. Estimation of equilibrium constants.

A simulation is developed that qualitatively describes the small-zone-gel-filtration behaviour of a reversibly associating protein. The results reflect the dependence of the apparent molecular weight of a reversibly associating protein on the equilibrium constant (KD) and initial concentration of the protein as well as the column length. The behaviour of a protein on an individual column is characterized and thus a means is provided for estimation of KD. The procedure is extended to describe the behaviour of a mixture of two proteins capable of heterologous as well as homologous association. This computer simulation has been applied in association studies of immunoglobulin light chains [Stevens, Westholm, Solomon & Schiffer (1980) Proc. Natl. Acad. Sci. 77, 1144--1148]. The KD value determined for the Bence--Jones protein Au (10(5) M-1) is close to the value (6.6 X 10(4) M-1) determined by other methods [Maeda, Steffen & Engel (1978) Biophys. Chem. 9, 57-64].

Bence Jones Protein↗
PubMed1980

Self-association of human immunoglobulin kappa I light chains: role of the third hypervariable region.

Gel electrophoresis and molecular sieve chromatography were used to compare 17 different human kappa I type Bence Jones proteins including 5 for which the amino acid sequence is known. Although electrophoresis in the presence of NaDodSO4 showed uniformity of covalent dimer and monomer molecular weights, Sephadex chromatography under nondissociating conditions showed that monomers eluted with different apparent molecular weights. These differences were attributed to heterogeneity in light chain self-association; dimerization constants of the 17 proteins, calculated from a computer simulation of their behavior upon gel filtration, ranged from less than 10(3) to greater than 10(6) M-1. The variable region, more specifically the third hypervariable region, appears to be responsible for the variation in the dimerization constant. Association properties of light chains of known sequence suggest that the presence of an aromatic or hydrophobic residue at position 96 enhances dimer formation whereas a charged residue at that position results in light chains remaining stable monomers. The location of hypervariable residue 96 within the amino-terminal portion of the joining segment of the variable region suggests that the joining region may account for the variability of self-association of light chains and, moreover, that it has a function in determining the selective association of immunoglobulin polypeptide chains.

Amino Acid Sequence↗