Pr. Erickson et Mc. Herzberg, ALTERED EXPRESSION OF THE PLATELET AGGREGATION-ASSOCIATED PROTEIN FROM STREPTOCOCCUS-SANGUIS AFTER GROWTH IN THE PRESENCE OF COLLAGEN, Infection and immunity, 63(3), 1995, pp. 1084-1088
Certain strains of Streptococcus sanguis adhere selectively to human p
latelets (Adh(+)) and, in plasma, induce them to aggregate into in vit
ro thrombi (Agg(+)). The induction of aggregation is mediated by the p
latelet aggregation-associated protein (PAAP) expressed on the cell su
rface of the streptococcus. In endocarditis, expression of PAAP may be
regulated by association with host proteins on damaged heart valves.
To begin to test this hypothesis, three strains of S. sanguis were eac
h cultured in the presence or absence of collagens (types I to X), lam
inin, or PAAP-derived peptide preparations. After harvesting and washi
ng, the platelet-interactive phenotype of strains 133-79 (Adh(+) Agg()), L74 (Adh(+) Agg(-)), and 10556 (Adh(-) Agg(-)) was unchanged. The
cells from each culture were then digested mildly with trypsin to isol
ate PAAP. PAAP isolated from strain 133-79 (Adh(+) Agg(+)) grown in th
e absence of added collagen, other proteins, or peptides inhibited pla
telet aggregation in response to untreated cells of S. sanguis. Platel
et aggregation was induced immediately however, by PAAP from strain 13
3-79 isolated after growth in the presence of 300 nM type I collagen,
while lower concentrations yielded protein fragments that potentiated
the response to intact cells. Aggregation-inducing PAAP could be remov
ed by anti-PAAP (PGEQGPK) immunoaffinity chromatography, but only inhi
bitory activity could be recovered. The agonist effect of PAAP was not
associated with collagen itself, since the PAAP preparations did not
contain detectable amounts of hydroxyproline. PAAP antigens isolated f
rom cells grown in the presence and absence of collagen had similar ap
parent molecular weights, as estimated by sodium dodecyl sulfate-polya
crylamide gel electrophoresis and Western immunoblotting. When electro
phoresis was performed under nondenaturing conditions, however, PAAP i
solated from cells grown in type I collagen migrated more slowly. Stra
in L74 grown with type I collagen yielded tryptic fragments of protein
s that inhibited aggregation significantly better than control peptide
s (no collagen in the medium). Strain 10556 was apparently unaffected
by growth in type I collagen. The effect of type I collagen was somewh
at unique. Growth in the presence of collagen types II to VI (300 nM)
yielded protein fragments that potentiated without inducing platelet a
ggregation, while other collagens, laminin, and PAAP-derived peptides
did not affect platelet aggregation. These results suggest that growth
in the presence of type I collagen and, perhaps, collagens II to VI a
lters the expression and conformation of PAAP in certain strains of S.
sanguis.