J. Soppa et al., BACTERIOOPSIN, HALOOPSIN, AND SENSORY OPSIN-I OF THE HALOBACTERIAL ISOLATE HALOBACTERIUM SP STRAIN-SG1 - 3 NEW MEMBERS OF A GROWING FAMILY, Journal of bacteriology, 175(9), 1993, pp. 2720-2726
The genes coding for bacterioopsin, haloopsin, and sensory opsin I of
a halobacterial isolate from the Red Sea called Halobacterium sp. stra
in SG1 have been cloned and sequenced. The deduced protein sequences w
ere aligned to the previously known halobacterial retinal proteins. Th
e addition of these new sequences lowered the number of conserved resi
dues to only 23 amino acids, or 8% of the alignment. Data base searche
s with two highly conserved peptides as well as with an alignment prof
ile yielded no significant similarity to any other protein, so the hal
obacterial retinal proteins should be regarded as a distinct protein f
amily. The protein alignment was used to make predictions about the st
ructure of the retinal proteins as well as about the amino acids in co
ntact with retinal proteins. These results were in excellent agreement
with the structural model of bacteriorhodopsin of Halobacterium halob
ium as well as with mutant studies, indicating that (i) structure pred
ictions based on the sequences of a membrane protein family can be qui
te accurate; (ii) halorhodopsin and sensory rhodopsin I have tertiary
structures similar to that of bacteriorhodopsin; (iii) conserved amino
acids do not take part in reactions specific for one group of protein
s, e.g., proton translocation for bacteriorhodopsins, but have a cruci
al role in determining the conformation and reactions of the chromopho
re; and (iv) the general mode of action (light-induced chromophore and
protein movements) is the same for all halobacterial retinal proteins
, ion pumps as well as sensors.