Hsu M, Scheid A, Choppin P W
J Biol Chem. 1981 Apr 10;256(7):3557-63.
The F protein of paramyxoviruses is actively involved in the induction of membrane fusion. This fusion may be between viral and cellular membranes, as in the initiation of infection or in virus-induced lysis of erythrocytes, or between the plasma membranes of different cells. The F protein is activated by proteolytic cleavage to yield two disulfide-linked polypeptides (F1 and F2); however, its mechanism of action is not clear. In the present study, the conformations of the inactive, uncleaved precursor of glycoprotein (F0), and the active, cleaved form (F1,2) have been compared. The UV circular dichroism spectra of the two forms of the F protein indicate that cleavage results in a conformational change. Detergent-binding studies by velocity sedimentation analysis of Triton X-100-protein complexes revealed an increase in exposed hydrophobic surface of the protein on cleavage. The inactive F0 bound an estimated 27 molecules of Triton X-100/F polypeptide; these molecules are presumably bound to the hydrophobic region of the glycoprotein that anchors the spike-like protein in the virus membrane and that is common to both forms of F. The active form, F1,2, bound 67 molecules of Triton X-100. This increase in the number of detergent binding sites upon F protein activation indicates the presence of a hydrophobic region that is peculiar to the active form, and that may be of functional significance in the membrane fusion reaction.
副粘病毒的F蛋白积极参与膜融合的诱导过程。这种融合可能发生在病毒膜与细胞膜之间，如在感染起始阶段或病毒诱导的红细胞裂解过程中，也可能发生在不同细胞的质膜之间。F蛋白通过蛋白水解切割被激活，产生两个通过二硫键连接的多肽（F1和F2）；然而，其作用机制尚不清楚。在本研究中，对糖蛋白无活性、未切割的前体（F0）和有活性、已切割的形式（F1,2）的构象进行了比较。F蛋白两种形式的紫外圆二色光谱表明，切割导致了构象变化。通过对Triton X-100-蛋白复合物进行速度沉降分析的去污剂结合研究显示，切割后蛋白质暴露的疏水表面增加。无活性的F0结合了大约27个Triton X-100/F多肽分子；这些分子大概结合在糖蛋白的疏水区域，该区域将刺突状蛋白锚定在病毒膜中，并且是两种F形式共有的。有活性的形式F1,2结合了67个Triton X-100分子。F蛋白激活后去污剂结合位点数量的增加表明存在一个活性形式特有的疏水区域，并且该区域可能在膜融合反应中具有功能意义。
