J Biol Chem, Vol. 273, Issue 6, 3291-3295, February 6, 1998
Different Endosomal Proteolysis Requirements for Antigen
Processing of Two T-cell Epitopes of the M5 Protein from Viable
Streptococcus pyogenes
Alexei A.
Delvig and
John H.
Robinson
From the Department of Immunology, School of Microbiological,
Virological, and Immunological Sciences, The Medical School, University
of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne,
Tyne and Wear, NE2 4HH, United Kingdom
We studied endosomal proteolysis of the surface
fibrillar M5 protein from viable Streptococcus pyogenes as
an essential step involved in major histocompatibility complex class
II-restricted antigen processing of two immunodominant CD4+
T-cell epitopes (17-31/Ed and 308-319/Ad).
Intracellular proteolysis of viable streptococci for presentation of
17-31, bound by serine proteinase cleavage sites, was mediated by
serine proteinases, whereas processing of soluble recombinant M5
protein required in addition cysteine proteinases. Furthermore, processing of 17-31 was resistant to ammonium chloride and thus was
not dependent on endosome acidification. Cysteine and serine proteinase
cleavage sites were located adjacent to 308-319, and its processing
was dependent on serine, cysteine, and aspartic proteinases, as well as
on endosomal acidification. The data suggest that antigen
processing of two major T-cell epitopes on streptococcal M5 protein
occurred in different endosomal compartments by different classes
of intracellular proteinases.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.