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The amino acid sequences of the Fd fragments of two human gamma-1 heavy chains.

ABSTRACT: The amino acid sequences of the Fd fragments of two human pathological immunoglobulins of the immunoglobulin G1 class are reported. Comparison of the two sequences shows that the heavy-chain variable regions are similar in length to those of the light chains. The existence of heavy chain variable region subgroups is also deduced, from a comparison of these two sequences with those of another gamma 1 chain, Eu, a mu chain, Ou, and the partial sequence of a fourth gamma 1 chain, Ste. Carbohydrate has been found to be linked to an aspartic acid residue in the variable region of one of the gamma 1 chains, Cor.

SUBMITTER: Press EM

PROVIDER: S-EPMC1179015 | biostudies-other | 1970 May

REPOSITORIES: biostudies-other

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Project description:Amino acid side-chain conformational properties influence the overall structural and dynamic properties of proteins and, therefore, their biological functions. In this study, quantum mechanical (QM) potential energy surfaces for the rotation of side-chain ?(1) and ?(2) torsions in dipeptides in the alphaR, beta, and alphaL backbone conformations were calculated. The QM energy surfaces provide a broad view of the intrinsic conformational properties of each amino acid side-chain. The extent to which intrinsic energetics dictates side-chain orientation was studied through comparisons of the QM energy surfaces with ?(1) and ?(2) free energy surfaces from probability distributions obtained from a survey of high resolution crystal structures. In general, the survey probability maxima are centered in minima of the QM surfaces as expected for sp(3) (or sp(2) for ?(2) of Asn, Phe, Trp, and Tyr) atom centers with strong variations between amino acids occurring in the energies of the minima indicating intrinsic differences in rotamer preferences. High correlations between the QM and survey data were found for hydrophobic side-chains except Met, suggesting minimal influence of the protein and solution environments on their conformational distributions. Conversely, low correlations for polar or charged side-chains indicate a dominant role of the environment in stabilizing conformations that are not intrinsically favored. Data also link the presence of off-rotamers in His and Trp to favorable interactions with the backbone. Results also suggest that the intrinsic energetics of the side-chains of Phe and Tyr may play important roles in protein folding and stability. Analyses on whether intrinsic side-chain energetics can influence backbone preference identified a strong correlation for residues in the alphaL backbone conformation. It is suggested that this correlation reflects the intrinsic instability of the alphaL backbone such that assumption of this backbone conformation is facilitated by intrinsically favorable side-chain conformations. Together our results offer a broad overview of the conformational properties of amino acid side-chains and the QM data may be used as target data for force field optimization.

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The amino acid sequences of the Fd fragments of two human gamma-1 heavy chains.

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