Journal of Experimental Medicine, Vol 147, 1771-1778, Copyright © 1978 by Rockefeller University Press
Streptococcal M protein extracted by nonionic detergent. III. Correlation between immunological cross-reactions and structural similarities with implications for antiphagocytosis
VA Fischetti
Three immunologically cross-reactive and non-cross-reactive streptococcal M
proteins were analyzed by a chromatographic tryptic peptide mapping system.
The results indicate that cross-reactions correlate with the extent of
structural similarity among the M protein molecules analyzed. The data also
reveal that free lysine is released by the action of trypsin from these
three M proteins, suggesting a common lys-lys or arg-lys sequence. In
addition, only one peptide has been found to be common within all three M
types. This limited structural relatedness among the three M proteins
examined indicates that sequence variation plays a major role in the
immunological specificity of the M antigens. However, despite sequence
variation, all M protein molecules have a common antiphagocytic activity.
The fact that no common opsonic antibody has yet been found, even against
limited M types, argues against this biological activity being solely the
result of a common sequence. Based on these data, it is suggested that the
antiphagocytic effect of M protein may be due to a conformationally created
environment on the surface of the molecule which is selected by both
immunological and biological pressure.
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