Hydrophobicity of Reactive Site Loop of SCCA1 Affects its Binding to HBV
鳞片状细胞癌抗原Ⅰ与乙型肝炎病毒的结合受反应位点环域疏水性的影响

Squamous cell carcinoma antigen 1 (SCCA1), a member of the ovalbumin family of serine protease inhibitors, includes several variants. It was reported that expression of two SCCA1 (BP and AJ515706) in cells results in increased binding of HBV to these cells by the interaction of the expressed BP and AJ515706 with HBV pre S1 domain. In this study, a SCCA1 (A1) was isolated from HepG2, but it appears to lack this ability. A possible role of two mutants, A1 BP and BP A1, constructed by interchanging the carboxyl terminal of A1 and BP, was investigated. Cells expressing A1 BP rather than BP A1 showed an increased virus binding capacity. Comparison of A1 sequence with the sequence of BP indicated the presence of only three amino acid changes in the carboxyl terminal, two of them in the reactive site loop (RSL) of SCCA1 Primary structure analysis revealed that the hydrophobicity of BP and AJ515706 in this domain is higher than that of A1 Changing the aa349 of A1 from low hydrophobic glutamic acid to high hydrophobic valine enhanced HBV binding. In contrast, changing the aa349 of BP from valine to glutamic acid reduced HBV binding. Our finding suggests that the hydrophobicity of RSL of SCCA1 may play an important role in HBV binding to cells.