Crystal structure of galactan-binding mouse immunoglobulin J539 Fab at 4.5-A resolution.

Self Cite

222

165

Human neutrophil elastase (HNE) has been implicated as a major contributor to tissue destruction in various disease states, including emphysema. The structure of HNE, at neutral pH, in complex with methoxysuccinylAla-Ala-Pro-Ala chloromethyl ketone (MSACK), has been solved and refmed to an R factor of 16.4% at 1.84-A resolution.Results are consistent with the currently accepted mechanism of peptide chloromethyl ketone inhibition of serine proteases, in that MSACK cross-links the catalytic residues His-57 and Ser-195. The structure of the HNE-MSACK complex is compared with that of porcine pancreatic elastase in complex with L-647,957, a fi-lactam inhibitor of both elastases. The distribution of positively charged residues on HNE is highiy asymmetric and may play a role in its specific association with the underlying negatively charged proteoglycan matrix of the neutrophil granules in which the enzyme is stored.

supporting

confidence: 66%

“…atic six-dimensional real-space rotation and translation search (22,23) was carried out by using the coordinates of the related structure of PPE. PPE had been refined at 1.84-A resolution by a restrained least-squares procedure (24) to an R factor of 16.5% (J.P.S.…”

mentioning

confidence: 99%

Structure of human neutrophil elastase in complex with a peptide chloromethyl ketone inhibitor at 1.84-A resolution.

Navia

McKeever

Springer

et al. 1989

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222

165

“…Antibodies to f3-(1,6)-galactan-containing antigens have been used in this laboratory as models for antibody-antigen interactions (27,28), idiotypy (26,29), diversity (10,24,26,30), and three-dimensional structure (31,32). The current investigation involves an analysis of three hybridoma proteins derived from a fusion of 2 BALB/c spleens with the nonsecreting Sp2/0 cell line (24).…”

Section: Resultsmentioning

confidence: 99%

Somatic diversification of immunoglobulins.

Rudikoff¹,

Pawlita²,

Pumphrey³

et al. 1984

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A series of three IgM, K monoclonal antibodies arising from a fusion of BALB/c spleen cells from mice immunized with j3-(1,6)-galactan-containing antigens have been analyzed. These three lines were found (i) to have homologous protein sequences in the heavy chain D region and at the sites of recombination between the heavy chain variable and D segment (VH-D) and the D and joining segment (D-JH), although amino acid substitutions were observed in both the heavy and light chain variable regions; (ii) to use identical heavy and light chain joining segments; and (iii) to demonstrate two identical (productive and nonproductive) K-chain rearrangements. A likely explanation for these observations is that the three lines are clonally related (arise from a common precursor) and that the observed heavy and light chain variable segment substitutions represent somatic point mutations. Because these antibodies are all of the IgM class, the results indicate that a somatic mutational mechanism is activated early in B-cell ontogeny and operates at both the heavy and light chain loci. Furthermore, the somatic mutation process appears to continue during the development of a given cell line, but is independent of class switching.Immunoglobulins are encoded by large multigene families that potentially express an almost unlimited degree of diversity at the level of serum antibody. It is now clear that a number of processes contribute to this phenomenon. First, there are an apparently large number of light (L)-and heavy (H)-chain germ-line variable (V)-region genes (1-4). Second, both L and H chains are encoded by multiple genetic elements: VK and JK in the L chain (5, 6) and VH, D, and JH (7,8) in the heavy chain. The number of protein structures that can be generated by various combinations of these segments constitutes a major portion of the total diversity. Third, the joining of the various gene segments is imprecise, creating sequence variation at the points of recombination (5,6,(9)(10)(11)(12). Fourth, interaction (i.e., gene conversion) may occur between related members of immunoglobulin families (13-15). Fifth, somatic point mutation provides an additional means by which structural alterations can be generated (16)(17)(18)(19)(20)(21)(22)(23).The last of the above mentioned processes, somatic mutation, has been a subject of interest and controversy in immunology for a number of years. Early studies in mouse X chains (16,17) provided the first evidence for somatic mutation and revealed a concentration of such mutations in complementarity-determining regions (CDR). Subsequent experiments in other systems have further documented the occurrence of somatic mutation in immunoglobulin genes, but it is presently unclear whether this process is random or directed to specific regions. While little is actually known about the precise mechanism and time of occurrence of somatic mutation in lymphocyte ontogeny, studies in two systems (19-21) have suggested that somatic mutation is linked, in some manner, to class switching in th...

“…The A light-chain dimer Loc represented the second intact Bence Jones protein to be successfully analyzed crystallographically (12). The protein, when crystallized from ammonium sulfate, exhibited a confornvation distinct from that of the previously studied light-chain dimer, Mcg (7), and several Fabs (16,(41)(42)(43)(44)(45). In Loc, a translation and rotation of domains resulted in the formation ofwhat was described as a protruding binding site (12), rather than the classic (canonical) concave binding pocket.…”

mentioning

confidence: 99%

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

Stevens

Chang

Schiffer

1988

The structure of an immunoglobulin antigenbinding fragment (Fab) has been thought to be invariantly defined by well-coiserved 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.Crystallographic studies of antigen-binding fragments (Fabs) have indicated that the principal determinants of quaternary structure are highly conserved domain-domain interactions (1)(2)(3)(4)(5) and that functional diversity originates from residue alternations, insertions, and deletions in segments of the heavy (H)-and light (L)-chain variable (V) domains designated hypervariable or complementarity determining regions (6). Several analogous studies with light-chain dimers have also supported the monomorphic conformation concept (7-10). However, in two instances (11,12), the observed Bence Jones protein conformations were anomalous; V-V domain interactions were found that had not been observed in Fabs. Although the relationships between these V domains were of significant interest in terms of the physical chemistry of antibody domain interactions, the physiological implications of the structures of the light-chain dimers formed by proteins Rhe (11)