Nozaki Y, Reynolds J A, Tanford C
Biochemistry. 1978 Apr 4;17(7):1239-46. doi: 10.1021/bi00600a017.
The coat protein of fd bacteriophage has a short polypeptide chain of only 50 amino acid residues, containing a highly hydrophobic segment of 19 amino acids that is entirely devoid of ionic or other strongly polar amino acids. In the viral particle the protein exists as a closely packed array of alpha helices. It can be transformed to a monomeric randomly coiled polypeptide in very concentrated (greater than or equal to 7.3 M) guanidinium chloride. In anionic detergents or phospholipids the protein is dimeric, with a mixed conformation ("50% alpha"), the hydrophobic segment having a beta structure, whereas the two ends are predominantly alpha helical. In guanidinium chloride at concentrations of 6 M or less, and under other conditions in the absence of an anionic detergent or phospholipid, the protein forms an intractable polymer, with a beta-type conformation. If the protein is succinylated an oligomeric form of this structure (speculatively thought to be a soluble variety of a "beta barrel") can be obtained as a metastable state. The 50% alpha conformation, the beta oligomer, and the random coil can be interconverted reversibly, but formation of the beta polymer appears to be irreversible.
fd噬菌体的外壳蛋白有一条仅由50个氨基酸残基组成的短多肽链，其中包含一段由19个氨基酸组成的高度疏水片段，该片段完全没有离子性或其他强极性氨基酸。在病毒颗粒中，该蛋白以紧密堆积的α螺旋阵列形式存在。在非常浓（大于或等于7.3M）的氯化胍中，它可以转变为单体无规卷曲多肽。在阴离子洗涤剂或磷脂中，该蛋白是二聚体，具有混合构象（“50%α”），疏水片段具有β结构，而两端主要是α螺旋。在浓度为6M或更低的氯化胍中，以及在没有阴离子洗涤剂或磷脂的其他条件下，该蛋白会形成难以处理的聚合物，具有β型构象。如果该蛋白被琥珀酰化，这种结构的寡聚形式（推测被认为是“β桶”的一种可溶变体）可以作为亚稳态获得。50%α构象、β寡聚体和无规卷曲可以可逆地相互转化，但β聚合物的形成似乎是不可逆的。
