Lengsin is a survivor of an ancient family of class I glutamine synthetases re-engineered by evolution for a role in the vertebrate lens.
Lengsin is a major protein of the vertebrate eye lens. It belongs to the hitherto purely prokaryotic GS I branch of the glutamine synthetase (GS) superfamily, but has no enzyme activity. Like the taxon-specific crystallins, Lengsin is the result of the recruitment of an ancient enzyme to a noncatalytic role in the vertebrate lens. Cryo-EM and modeling studies of Lengsin show a dodecamer structure with important similarities and differences with prokaryotic GS I structures. GS homology regions of Lengsin are well conserved, but the N-terminal domain shows evidence of dynamic evolutionary changes. Compared with birds and fish, most mammals have an additional exon corresponding to part of the N-terminal domain; however, in human, this is a nonfunctional pseudoexon. Genes related to Lengsin are also present in the sea urchin, suggesting that this branch of the GS I family, supplanted by GS II enzymes in vertebrates, has an ancient role in metazoans.
Wyatt
Keith
K
Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
White
Helen E
HE
Wang
Luchun
L
Bateman
Orval A
OA
Slingsby
Christine
C
Orlova
Elena V
EV
Wistow
Graeme
G
D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D020285:Cryoelectron Microscopy; D019143:Evolution, Molecular; D005136:Eye Proteins / Q000378:metabolism / Q000502:physiology*; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D051381:Rats; D012617:Sea Urchins; D017386:Sequence Homology, Amino Acid
D005136:Eye Proteins; D005974:Glutamate-Ammonia Ligase; C507977:LGSN protein, human