Structure-function studies of bacteriorhodopsin XV. Effects of deletions in loops B-C and E-F on bacteriorhodopsin chromophore and structure.
Bacteriorhodopsin mutants containing deletions in loop B-C, delta Thr67-Glu74 or delta Gly65-Gln75 or a deletion in the loop E-F, delta Glu161-Ala168, were prepared. Following their expression in Escherichia coli, the mutant proteins were purified to homogeneity and refolded with retinal in detergent-phospholipid mixtures. The mutants containing deletions in the loop B-C were normal at 4 degrees C but showed the following changes at 20 degrees C. 1) The lambda max shifted from 540 to below 510 nm; 2) the rates of bleaching by hydroxylamine in the dark increased; and 3) the rate and steady state of proton pumping decreased. Deletion of the eight amino acids in loop E-F did not affect wild-type behavior. However, all the mutant proteins were more prone to thermal and sodium dodecyl sulfate denaturation than the wild-type bacteriorhodopsin. These observations show that the structures of the B-C and E-F loops are not essential for correct folding of bacteriorhodopsin, but they contribute to the stability of the folded protein.
Gilles-Gonzalez
M A
MA
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Engelman
D M
DM
Khorana
H G
HG
D000595:Amino Acid Sequence; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D002872:Chromosome Deletion; D002942:Circular Dichroism; D004926:Escherichia coli / Q000235:genetics; D007700:Kinetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011489:Protein Denaturation; D012967:Sodium Dodecyl Sulfate; D013329:Structure-Activity Relationship; D013696:Temperature
D012967:Sodium Dodecyl Sulfate; D001436:Bacteriorhodopsins