Navon A, Schulze A J, Guillou Y, Zylinski C A, Baleux F, Expert-Bezançon N, Friguet B, Djavadi-Ohaniance L, Goldberg M E
Department of Life Sciences, Bar Ilan University, Ramat Gan, Israel.
J Biol Chem. 1995 Mar 3;270(9):4255-61. doi: 10.1074/jbc.270.9.4255.
The epitope recognized by a monoclonal antibody (mAb19) directed against the beta 2 subunit of Escherichia coli tryptophan synthase was found to be carried by residues 2-9 of the beta chain. The affinities of mAb19 for peptides of different lengths containing the 2-9 sequence were close to 0.6 x 10(9) M-1, the affinity of mAb19 for native beta 2. In view of these results, a model is proposed to account for the kinetics of appearance of the epitope during in vitro renaturation of beta 2 (Murry-Brelier, A., and Goldberg, M.E. (1988) Biochemistry 27, 7633-7640). A mutant producing beta chains lacking residues 1-9 (beta delta 1-9) was prepared. The beta delta 1-9 protein was able to fold into a heat stable homodimer resembling wild type beta 2. Isolated beta delta 1-9 had no detectable enzymatic activity. It could bind alpha chains extremely weakly and be slightly activated. In the presence of the 1-9 peptide, the beta delta 1-9 protein could bind alpha chains much more strongly and generate a 50% active enzyme. Thus, although having little role in the overall folding and stability of the protein, the 1-9 sequence of the beta chain appears strongly involved in the alpha-beta interactions and in the enzymatic activity.
一种针对大肠杆菌色氨酸合酶β2亚基的单克隆抗体（mAb19）所识别的表位，被发现由β链的2 - 9位残基携带。mAb19对包含2 - 9序列的不同长度肽段的亲和力接近0.6×10⁹ M⁻¹，即mAb19对天然β2的亲和力。鉴于这些结果，提出了一个模型来解释β2在体外复性过程中表位出现的动力学（默里 - 布雷利尔，A.，和戈德堡，M.E.（1988年）《生物化学》27，7633 - 7640）。制备了一种产生缺失1 - 9位残基的β链（βδ1 - 9）的突变体。βδ1 - 9蛋白能够折叠成一种类似于野生型β2的热稳定同源二聚体。分离出的βδ1 - 9没有可检测到的酶活性。它与α链的结合极其微弱，且仅有轻微激活。在1 - 9肽存在的情况下，βδ1 - 9蛋白与α链的结合能力更强，能产生50%活性的酶。因此，尽管β链的1 - 9序列在蛋白质的整体折叠和稳定性方面作用不大，但它似乎在α - β相互作用和酶活性中起着重要作用。
