Characterization of recombinant Streptococcus mitis-derived human platelet aggregation factor

Ohkuni H, Nagamune H, Ozaki N, Tabata A, Todome Y, Watanabe Y, Takahashi H, Ohkura K, Kourai H, Ohtsuka H, Fischetti VA, Zabriskie JB. Characterization of recombinant Streptococcus mitis‐derived human platelet aggregation factor. APMIS 2012; 120: 56–71. We previously purified Streptococcus mitis‐derived human platelet aggregation factor (Sm‐hPAF) from the culture supernatant of S. mitis strain Nm‐65, isolated from the tooth surface of a patient with Kawasaki disease. Here we produced recombinant Sm‐hPAF protein (rSm‐hPAF) in Escherichia coli, to determine whether rSm‐hPAF conserves its platelet aggregation activity. rSm‐hPAF precursor (665 amino acids) shows up to 36–56% identity with the family of cholesterol‐dependent cytolysins (CDCs), and rSm‐hPAF displayed potent hemolytic activity toward mammalian erythrocytes, including human erythrocytes with platelet aggregation activity. The 162‐amino acid amino‐terminal domain of rSm‐hPAF was found in no other CDCs except lectinolysin; this domain is homologous to a portion of pneumococcal fucolectin‐related protein. Interestingly, suilysin (SLY) and pneumolysin (PLY) of CDCs also exhibit substantial human platelet aggregation activity, similar to rSm‐hPAF, and the platelet aggregation by rSm‐hPAF, SLY, and PLY was morphologically confirmed using light and electron microscopy.