Determination of the primary structure of cholera toxin B subunit

The primary structure of cholera toxin B subunit, responsible for the binding of the toxin to cell surface ganglioside Gm1, has been determined as: Thr-Pro-Gln-Asn-Ile-Thr-Asp-Leu-Cys-Ala-Glu-Tyr-His-Asn-Thr-Gln-Ile-His-Thr-Leu-Asn-Asn-Lys-Ile-Phe-Ser-Tyr-Thr-Glu-Ser-Leu-Ala-Gly-Lys-Arg-Glu-Met-Ala-Ile-Ile-Thr-Phe-Lys-Asn-Gly-Ala-Thr-Phe-Glu-Val-Glu-Val-Pro-Gly-Ser-Gln-His-Ile-Asp-Ser-Gln-Lys-Lys-Ala-Ile-Glu-Arg-Met-Lys-Asn-Thr-Leu-Arg-Ile-Ala-Tyr-Leu-Thr-Glu-Ala-Lys-Val-Glu-Lys-Leu-Cys-Val-Trp-Asn-Asn-Lys-Thr-Pro-His-Ala-Ile-Ala-Ala-Ile-Ser-Met-Ala-Asn The number and the sequence of amino acid residues has been established by separation and analyses of the peptides obtained through enzymatic and chemical cleavage of the B subunit. The chymotryptic peptides from the citraconylated B subunit proved to be useful in the alignment of the tryptic peptide.

Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide

The amino acid sequence of a biologically active polypeptide isolated from calf thymus, termed thymosin alpha1, has been determined. Thymosin alpha1 is a heat stable, highly acidic molecule composed of 28 amino acid residues. This peptide is one of several present in thymosin fraction 5 that may participate in the regulation, differentiation and function of thymus-dependent lymphocytes (T cells). A nomenclature for the family of polypeptides present in thymosin fraction 5 is suggested.

Chemistry of cholera toxin: the subunit structure

The toxin of Vibrio cholerae was separated into two subunits by gel filtration on Sephadex G-75 in 5% formic acid. The subunits were designated A and B. Amino acid analysis indicated that subunit B corresponded to choleragenoid. Renatured subunit B was found to be antigenically identical to the whole molecule, whereas renatured subunit A was not. On reduction and S-carboxymethylation with [2-14C] iodoacetate in 8 m urea, subunit A separated into two polypeptides of unequal sizes, A1 and A2, with equal amounts of radioactivity. Subunit B, on the other hand, remained a single molecular species. Molecular weights of the polypeptides A1, A2, and B were estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate-urea buffer, in conjunction with amino acid analysis, to be 20,000, 7,500, and 9,500 daltons, respectively. The carboxyl terminal sequence of subunit B was found to be -Met-Ala-Asn. After treatment of toxin with cyanogen bromide, the peptide Ala-Asn could be isolated and quantitated. From this data the number of B polypeptides in a molecule of toxin was estimated as six.

Amino acid sequence of rabbit muscle aldolase and the structure of the active center

Elucidation of the amino acid sequence of fructose-1,6-bis-phosphate aldolase from rabbit muscle has made it possible to assign the positions of the functional groups known to play specific roles in the catalytic activity, and also to locate the buried, exposed, and active site cysteine residues. The results indicate that the middle portion of the polypeptide chain, including Cys-134, Cys-149, Cys-177, and Cys-l99, is buried in the native structure, with regions containing Cys-72, Lys-107, Lys-227, Cys-336, His-359, and the COOH-terminal residue (Tyr-361) folded into the active center of the enzyme, at or near the surface of the enzyme molecule.