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Pharaonis Phoborhodopsin Binds to its Cognate Truncated Transducer Even in the Presence of a Detergent with a 1:1 Stoichiometry ¶
Author(s) -
Sudo Yuki,
Iwamoto Masayuki,
Shimono Kazumi,
Kamo Naoki
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0740489ppbtic2.0.co2
Subject(s) - dissociation constant , histidine , chemistry , exponential decay , dissociation (chemistry) , phototaxis , cytoplasm , binding site , crystallography , stoichiometry , biophysics , stereochemistry , receptor , biochemistry , biology , amino acid , physics , botany , nuclear physics
Pharaonis phoborhodopsin ( p pR) (also pharaonis sensory rhodopsin II) is a receptor of the negative phototaxis of Natronobacterium pharaonis. p pR forms a complex with its pharaonis halobacterial transducer (pHtrII), and this complex transmits the light signal to the sensory system in the cytoplasm. The expressed C‐terminal‐His tagged p pR and C‐terminal‐His tagged truncated pHtrII (t‐Htr) in Escherichia coli (His means the 6× histidine tag) form a complex even in the presence of 0.1% of n ‐dodecyl‐β‐ d ‐maltoside, and the M‐decay of the complex became about twice slower than that of p pR alone. The photocycling rates under varying concentration ratios of p pR to t‐Htr in the presence of detergent were measured. The data were analyzed on the following assumptions: (1) the M‐decay of both p pR alone and the complex followed a single exponential decay with different time constants; and (2) the M‐decay under varying concentration ratios of p pR to t‐Htr, therefore, followed a biexponential decay function which combined the decay of the free p pR and that of the complex as photoreactive species. From these analyses we estimated the dissociation constant (15.2 ± 1.8 μ M ) and the number of binding sites (1.2 ± 0.08).