EB病毒蛋白BNLF2a阻止抗原转运蛋白TAP的构象变化

Epstein-Barr viral protein BNLF2a suppresses the conformational change of antigenic peptide transporter TAP

摘要:

【背景】EB病毒是一个常见的病原，它能引起霍奇金淋巴瘤、伯基特淋巴瘤以及胃癌、鼻咽癌。该病毒编码的膜蛋白BNLF2a抑制抗原转运蛋白TAP (transporter associated with antigen processing)从而逃逸T细胞的清除。TAP属于ABC (ATP-binding cassette)转运蛋白超家族，是由TAP1和TAP2两个亚基构成的。TAP通过ATP提供能量，跨膜转运抗原多肽，这一过程伴随着构象变化。【目的】旨在揭示BNLF2a是否影响TAP的构象变化。【方法】TAP蛋白核酸结合结构域的二聚体界面的D-loop进行点突变，引入半胱氨酸。在表达和不表达BNLF2a情况下，采用氧化性的二价铜离子交联半胱氨酸，并通过western blot对比TAP的半胱氨酸形成二硫键的比例。【结果】BNLF2a表达使TAP被交联的比例增高。【结论】BNLF2a可能将TAP稳定在核苷酸结合结构域二聚化的构象，从而同时抑制ATP和抗原多肽结合到TAP上来。

关键词:EB病毒，BNLF2a，TAP，ABC转运蛋白，抗原多肽

Abstract:

[Background] Epstein-Barr virus (EBV) is a common pathogen causing Burkitt’s lymphoma, Hodgkin’s disease, gastric cancer and nasopharyngeal carcinoma. A membrane protein BNLF2a encoded by EBV inhibits antigen transportation by transporter associated with antigen processing (TAP) and thereby evades the elimination by cytotoxic T cells. TAP is a member of the ATP-binding cassette (ABC) superfamily and composed of two subunits of TAP1 and TAP2. Using the energy of ATP hydrolysis, TAP transports antigenic peptides across the membrane with a conformational change. [Objective] The aim of this study was to study if BNLF2a affects the conformational switch of TAP. [Methods] Cysteines were introduced into the D-loop at the interface of TAP’s nucleotide binding domains. TAP were cross-linked by oxidizing agent Cu(II). The ratios of disulfide formed TAP were compared in the presence or absence of BNLF2a by western blot. [Results] The expression of BNLF2a increased the ratio of cross-linked TAP. [Conclusion] BNLF2a appears to stabilize TAP in the nucleotide binding domains dimerized conformation and thereby inhibit both of ATP and antigenic peptide binding to TAP.

Key words:EB virus, BNLF2a, TAP, ABC transporter, Antigenic peptide