NDLI: Molecular Evolutionary Analysis of Vertebrate Transducins: A Role for Amino Acid Variation in Photoreceptor Deactivation

Content Provider	Springer Nature Link
Author	Lin, Yi Weadick, Cameron J. Santini, Francesco Chang, Belinda S. W.
Copyright Year	2013
Abstract	Transducin is a heterotrimeric G protein that plays a critical role in phototransduction in the rod and cone photoreceptor cells of the vertebrate retina. Rods, highly sensitive cells that recover from photoactivation slowly, underlie dim-light vision, whereas cones are less sensitive, recover more quickly, and underlie bright-light vision. Transducin deactivation is a critical step in photoreceptor recovery and may underlie the functional distinction between rods and cones. Rods and cones possess distinct transducin α subunits, yet they share a common deactivation mechanism, the GTPase activating protein (GAP) complex. Here, we used codon models to examine patterns of sequence evolution in rod (GNAT1) and cone (GNAT2) α subunits. Our results indicate that purifying selection is the dominant force shaping GNAT1 and GNAT2 evolution, but that GNAT2 has additionally been subject to positive selection operating at multiple phylogenetic scales; phylogeny-wide analysis identified several sites in the GNAT2 helical domain as having substantially elevated dN/dS estimates, and branch-site analysis identified several nearby sites as targets of strong positive selection during early vertebrate history. Examination of aligned GNAT and GAP complex crystal structures revealed steric clashes between several positively selected sites and the deactivating GAP complex. This suggests that GNAT2 sequence variation could play an important role in adaptive evolution of the vertebrate visual system via effects on photoreceptor deactivation kinetics and provides an alternative perspective to previous work that focused instead on the effect of GAP complex concentration. Our findings thus further the understanding of the molecular biology, physiology, and evolution of vertebrate visual systems.
Starting Page	231
Ending Page	245
Page Count	15
File Format	PDF
ISSN	00222844
Journal	Journal of Molecular Evolution
Volume Number	77
Issue Number	5-6
e-ISSN	14321432
Language	English
Publisher	Springer US
Publisher Date	2013-10-22
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	G proteins Vision Rhodopsin dN/dS Positive selection Maximum likelihood Codon models Evolutionary Biology Microbiology Plant Sciences Plant Genetics & Genomics Animal Genetics and Genomics Cell Biology
Content Type	Text
Resource Type	Article
Subject	Genetics Molecular Biology Ecology, Evolution, Behavior and Systematics

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