Devaux C, Caillet-Boudin M L, Jacrot B, Boulanger P
European Molecular Biology Laboratory, Grenoble Outstation, France.
Virology. 1987 Nov;161(1):121-8. doi: 10.1016/0042-6822(87)90177-2.
Crystals of the fiber protein of adenovirus type 2 have been grown. Analysis of these crystals (type I crystals) showed that they were composed of fiber polypeptide with a lower apparent molecular weight (60 kDa) than that of the soluble or virion-incorporated fiber (62 kDa). N-terminal sequencing revealed that the fiber polypeptide chain of 60 kDa was cleaved at tyrosine17 from the N-end. The C-terminus remained intact. Assays with protease inhibitors suggested that the spontaneous cleavage of the fiber occurring upon its crystallization was due to a cellular, calcium-dependent, chymotrypsin-like protease co-purifying with the fiber and activated during hydroxyapatite chromatography. Crystallization of fiber purified in the presence of chymostatin provided crystals of a different structure under the electron microscope (crystals of type II), composed of 62-kDa fiber polypeptide units. The 62-kDa fiber from the type II crystals, as well as the 62-kDa fiber isolated from infected cell extracts, were able to associate with the penton base in vitro to form a penton capsomer. The 60-kDa fiber has lost this capacity. The accessibility of the N- and C-termini of the fiber inside the penton structure was probed by anti-peptide sera after limited proteolysis. The results are consistent with a polarity of the fiber in which its N-terminus is oriented toward the penton base, the C-terminal domain corresponding to the distal knob.
2型腺病毒纤维蛋白的晶体已生长出来。对这些晶体（I型晶体）的分析表明，它们由表观分子量（60 kDa）比可溶性或病毒体结合纤维（62 kDa）更低的纤维多肽组成。N端测序显示，60 kDa的纤维多肽链从N端的酪氨酸17处被切割。C端保持完整。用蛋白酶抑制剂进行的分析表明，纤维在结晶时发生的自发切割是由于一种与纤维共纯化并在羟基磷灰石色谱过程中被激活的细胞内钙依赖性类胰凝乳蛋白酶。在抑肽酶存在下纯化的纤维结晶在电子显微镜下呈现出不同结构的晶体（II型晶体），由62 kDa的纤维多肽单元组成。来自II型晶体的62 kDa纤维以及从感染细胞提取物中分离出的62 kDa纤维能够在体外与五邻体基部结合形成五邻体壳粒。60 kDa的纤维失去了这种能力。在有限蛋白酶解后，用抗肽血清探测了五邻体结构内纤维的N端和C端的可及性。结果与纤维的极性一致，即其N端朝向五邻体基部，C端结构域对应于远端球状结构。
