The L1 major capsid protein of human papillomavirus type 11 recombinant virus-like particles interacts with heparin and cell-surface glycosaminoglycans on human keratinocytes

The L1 major capsid protein of human papillomavirus (HPV) type 11, a 55-kDa polypeptide, forms particulate structures resembling native virus with an average particle diameter of 50-60 nm when expressed in the yeast Saccharom yces cerevisiae. me show in this report that these virus-like particles (VL Ps) interact with heparin and with cell-surface glycosaminoglycans (GAGs) r esembling heparin on keratinocytes and Chinese hamster ovary cells. The bin ding of VLPs to heparin is shown to exhibit an affinity comparable to that of other identified heparin-binding proteins. Immobilized heparin chromatog raphy and surface plasmon resonance were used to show that this interaction can be specifically inhibited by free heparin and dextran sulfate and that the effectiveness of the inhibitor is related to its molecular weight and charge density. Sequence comparison of nine human L1 types revealed a conse rved region of the carboxyl terminus containing clustered basic amino acids that bear resemblance to proposed heparin-binding motifs in unrelated prot eins. Specific enzymatic cleavage of this region eliminated binding to both immobilized heparin and human keratinocyte (HaCaT) cells. Removal of hepar an sulfate GAGs on keratinocytes by treatment with heparinase or heparitina se resulted in an 80-90% reduction of VLP binding, whereas treatment of cel ls with laminin, a substrate for cu, integrin receptors, provided minimal i nhibition. Cells treated with chlorate or substituted beta-D-xylosides, res ulting in under-sulfation or secretion of GAG chains, also showed a reduced affinity for VLPs. Similarly, binding of VLPs to a Chinese hamster ovary c ell mutant deficient in GAG synthesis was shown to be only 10% that observe d for wild type cells. This report establishes for the first time that the carboxyl-terminal portion of HPV L1 interacts with heparin, and that this r egion appears to be crucial for interaction with the cell surface.