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A family of clostridial and streptococcal ligand‐binding proteins with conserved C‐terminal repeat sequences
Author(s) -
Wren B. W.
Publication year - 1991
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1991.tb00752.x
Subject(s) - biology , glucosyltransferases , streptococcus mutans , lytic cycle , biochemistry , ligand (biochemistry) , enzyme , clostridium difficile toxin a , binding domain , amino acid , binding site , microbiology and biotechnology , genetics , bacteria , clostridium difficile , receptor , virus , antibiotics
Summary Analysis of the derived amino acid sequences of toxins A and B from Clostridium difficile has identified an extraordinarily large number of repeat amino acid units in the C ‐terminal regions of the proteins. Nearly one third of each of the proteins consist of repeating units which appear, at least in the case of toxin A, to be responsible for carbohydrate binding. Similar repeat units are also found in the C‐terminal region of four glucosyltransferases from Streptococcus mutans and Streptococcus downel , and in four lytic enzymes from Streptococcus pneumoniae and its bacteriophages (HB‐3, Cp‐1 and Cp‐9). In each case the repeats constitute the ligand‐binding portion of the respective enzymes. A glucan‐binding protein from S. mutans , which lacks enzymatic activity, has similar repeats spanning almost the entire molecule. This family of ligand‐binding proteins appears to be of modular design, with one module consisting of a repetitive ligand‐binding domain located in the C ‐terminal region and the other module(s) providing enzymatic functions.