Epistatic effects of the protease/chaperone HflB on some damaged forms of the Escherichia coli ammonium channel AmtB.
The Escherichia coli ammonium channel AmtB is a trimer in which each monomer carries a pore for substrate conduction and a cytoplasmic C-terminal extension of approximately 25 residues. Deletion of the entire extension leaves the protein with intermediate activity, but some smaller lesions in this region completely inactivate AmtB, as do some lesions in its cytoplasmic loops. We here provide genetic evidence that inactivation depends on the essential protease HflB, which appears to cause inactivation not as a protease but as a chaperone. Selection for restored function of AmtB is a positive selection for loss of the ATPase/chaperone activity of HflB and reveals that the conditional lethal phenotype for hflB is cold sensitivity. Deletion of only a few residues from the C terminus of damaged AmtB proteins seems to prevent HflB from acting on them. Either yields the intermediate activity of a complete C-terminal deletion. HflB apparently "tacks" damaged AmtB tails to the adjacent monomers. Knowing that HflB has intervened is prerequisite to determining the functional basis for AmtB inactivation.
Inwood
William B
WB
Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA.
Hall
Jason A
JA
Kim
Kwang-Seo
KS
Demirkhanyan
Lusine
L
Wemmer
David
D
Zgurskaya
Helen
H
Kustu
Sydney
S
D049069:ATP-Dependent Proteases / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004843:Epistasis, Genetic; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011487:Protein Conformation; D013489:Suppression, Genetic
C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D049069:ATP-Dependent Proteases; C513383:FtsH protein, E coli