[Identification of repetitive sequences and internal symmetry in primary structure of yeast GDP-Man:Dol-PP-GlcNAc2 mannosyltransferase].

Segments of the amino acid sequence containing a large number of internal symmetry centres were identified in the primary structure of enzyme GDP-Man:Dol-PP-GlcNAc2 mannosyltransferase (gene ALG1 product of yeast) by means of a comparative analysis of amino acid codon roots (AACR). The highest density of symmetric segments was discovered in the AlG1 N-terminal hydrophobic segment which is responsible for the enzyme anchoring in the membrane and contains a dolichol-binding sequence, and is one of the central (104-195) and C-terminal (310-439) segments of ALG1. Amino acid sequences 104-195 and 310-439, on the one hand, are structurally similar to carbohydrate-binding proteins (lectins) and so, may participate in formation of the catalytic enzyme centre that interacts with carbohydrate-containing substrates, GDP-mannose and Dol-PP-GlcNAc2, and, on the other hand, they are able to form some alpha-helices. These data agree with the supposition about evolutionary conservation of the symmetric structures in molecular segments of proteins, which determine their functional activity. The graphic method of the AACR sequence analysis suggested by the authors has permitted identifying repeating homologous sequences of 18-20 amino acids in the enzyme molecule. They are a result of DNA sequence duplication and multiplication in evolution. Moreover, two long segments (305-357 and 376-430) possessing (after alignment of their amino acid sequences) 21% identical and 64% equifunctional amino acid residues were found in the C-terminal region of ALG1. These data, probably, testify to duplication of the nucleotide sequence, coding these segments.