Zinc stabilizes the SecB binding site of SecA.

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.

[1]  W. Wickner,et al.  The SecA Subunit of Escherichia coliPreprotein Translocase Is Exposed to the Periplasm , 1998, Journal of bacteriology.

[2]  H. Koch,et al.  Requirements for the Translocation of Elongation-arrested, Ribosome-associated OmpA across the Plasma Membrane ofEscherichia coli * , 1998, The Journal of Biological Chemistry.

[3]  A. Driessen,et al.  The molecular chaperone SecB is released from the carboxy‐terminus of SecA during initiation of precursor protein translocation , 1997, The EMBO journal.

[4]  J. Lakowicz,et al.  Interaction of SecB with soluble SecA 1 , 1997, FEBS letters.

[5]  V. Ramamurthy,et al.  Topology of the Integral Membrane Form of Escherichia coli SecA Protein Reveals Multiple Periplasmically Exposed Regions and Modulation by ATP Binding* , 1997, The Journal of Biological Chemistry.

[6]  C. Kumamoto,et al.  Diverse Effects of Mutation on the Activity of the Escherichia coli Export Chaperone SecB (*) , 1995, The Journal of Biological Chemistry.

[7]  J. Tommassen,et al.  The C Terminus of SecA Is Involved in Both Lipid Binding and SecB Binding (*) , 1995, The Journal of Biological Chemistry.

[8]  L. Randall,et al.  High selectivity with low specificity: how SecB has solved the paradox of chaperone binding. , 1995, Trends in biochemical sciences.

[9]  C. Kumamoto,et al.  Highly selective binding of nascent polypeptides by an Escherichia coli chaperone protein in vivo , 1993, Journal of bacteriology.

[10]  A. Driessen,et al.  ProOmpA contains secondary and tertiary structure prior to translocation and is shielded from aggregation by association with SecB protein. , 1990, The EMBO journal.

[11]  C. Georgopoulos,et al.  Three pure chaperone proteins of Escherichia coli‐‐SecB, trigger factor and GroEL‐‐form soluble complexes with precursor proteins in vitro. , 1989, The EMBO journal.

[12]  J. Beckwith,et al.  Mutations in a new gene, secB, cause defective protein localization in Escherichia coli , 1983, Journal of bacteriology.

[13]  J. Berg.  Zinc Finger Domains: From Predictions to Design , 1995 .