Amino acid sequence of guinea pig liver transglutaminase from its cDNA sequence

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Abstract
Transglutaminases (EC 2.3.2.13) catalyze the formation of .epsilon.-(.gamma.-glutamyl)lysine cross-links and the substitution of a variety of primary amines for the .gamma.-carboxamide groups of protein-bound glutaminyl residues. These enzymes are involved in many biological phenomena. In this paper, the complete amino acid sequence of guinea pig liver transglutaminase, a typical tissue-type nonzymogenic transglutaminase, was predicted by the cloning and sequence analysis of DNA complementary to its mRNA. The cDNA clones carrying the sequences for the 5''-and 3''-end regions of mRNA were obtained by use of the sequence of the partial-length cDNA of guinea pig liver transglutaminase [Ikura, K., Nasu, T., Yokota, H., Sasaki, R., and Chiba, H. (1987) Agric. Biol. Chem. 51, 957-961]. A total of 3695 bases were identified from sequence data of four overlapping cDNA clones. Northern blot analysis of guinea pig liver poly(A+) RNA showed a single species of mRNA with 3.7-3.8 kilobases, indicating that almost all of the mRNA sequence was analyzed. The composite cDNA sequence contained 68 bases of a 5''-untranslated region, 2073 bases of an open reading frame that encoded 691 amino acids, a stop codon (TAA), 1544 bases of a 3''-noncoding region, and a part of a poly(A) tail (7 bases). The molecular weight of guinea pig liver transglutaminase was calculated to be 76 620 from the amino acid sequence deduced, excluding the initiator Met. This enzyme contained no carbohydrate [Folk, J.E., and Chung, S.I. (1973) Avd. Enzymol. Relat. Areas Mol. Biol. 38, 109-191], but six potential Asn-linked glycosylation sites were found inthe sequence deduced. The primary structure of guinea pig liver transglutaminase was compared with that of the catalytic a subunit of human factor XIII (zymogenic transglutaminase). Several regions of strong homology, including the region surrounding the active site cysteine residue, were observed. A hydropathy profile of the liver transglutaminase suggested that the active site cysteine residue was at the amino-terminal end of a highly hydrophobic region. Regions clearly having the "E-F-hand structure", a typical calcium-binding site, were not found in the sequence of the liver enzyme.