Fekkes P, de Wit J G, Boorsma A, Friesen R H, Driessen A J
Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Goningen, The Netherlands.
Biochemistry. 1999 Apr 20;38(16):5111-6. doi: 10.1021/bi982818r.
The molecular chaperone SecB targets preproteins to SecA at the translocation sites in the cytoplasmic membrane of Escherichia coli. SecA recognizes SecB via its carboxyl-terminal 22 aminoacyl residues, a highly conserved domain that contains 3 cysteines and 1 histidine residue that could potentially be involved in the coordination of a metal ion. Treatment of SecA with a zinc chelator resulted in a loss of the stimulatory effect of SecB on the SecA translocation ATPase activity, while the activity could be restored by the addition of ZnCl2. Interaction of SecB with the SecB binding domain of SecA is disrupted by chelators of divalent cations, and could be restored by the addition of Cu2+ or Zn2+. Atomic absorption and electrospray mass spectrometry revealed the presence of one zinc atom per monomeric carboxyl terminus of SecA. It is concluded that the SecB binding domain of SecA is stabilized by a zinc ion that promotes the functional binding of SecB to SecA.
分子伴侣SecB将前体蛋白转运至大肠杆菌细胞质膜转位位点处的SecA。SecA通过其羧基末端的22个氨酰基残基识别SecB，这是一个高度保守的结构域，含有3个半胱氨酸和1个组氨酸残基，它们可能参与金属离子的配位。用锌螯合剂处理SecA会导致SecB对SecA转位ATP酶活性的刺激作用丧失，而通过添加ZnCl₂可恢复该活性。SecB与SecA的SecB结合结构域之间的相互作用会被二价阳离子螯合剂破坏，添加Cu²⁺或Zn²⁺可恢复该相互作用。原子吸收光谱法和电喷雾质谱法显示，SecA的每个单体羧基末端存在一个锌原子。得出的结论是，SecA的SecB结合结构域由一个锌离子稳定，该锌离子促进SecB与SecA的功能性结合。
