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Peter A. Binkley, John Hess, Jodi Casselman, Paul FitzGerald; Unexpected Variation in Unique Features of the Lens-Specific Type I Cytokeratin CP49. Invest. Ophthalmol. Vis. Sci. 2002;43(1):225-235.
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purpose. CP49 is a fiber cell–specific type I cytokeratin, but its
function as part of the fiber cell–beaded filament remains unknown. To
provide a rational basis for mutational studies that would contribute
to an elucidation of function, the study was designed to define
elements of CP49s that are highly conserved, discriminate conserved
features from species-specific variations, and identify where CP49s
have diverged from consensus type I features in their adaptation to
selective pressures in the lens.
methods. The primary sequence and gene structure of CP49 from a third vertebrate
order was determined from a combination of cDNA and genomic sequencing.
Protein product was characterized by SDS-PAGE and Western blot
analysis. Consensus features and phylogenetic relationships were
identified by multiple alignment. Coiled-coil analysis was conducted to
define central rod domains.
results. Trout CP49 is unique among CP49s in having a 39-amino-acid tail domain
and shows both unique sequence and allelic variation at the LNDR motif.
Comparison of consensus sequences identified unprecedented divergence
between CP49s and other type I cytokeratins, including a shortened
central rod domain that is conserved among CP49s, but distinct from
type I cytokeratins.
conclusions. The considerable differences that have emerged between the consensus
features of the type I cytokeratins and the CP49s suggest that the
beaded filament serves a significantly different function from
intermediate filaments in other epithelia and that type I cytokeratins
may have limited utility as a model for studies on lens beaded
filaments. These differences, in concert with consensus features
identified among CP49s, suggest sites that are probably critical to
CP49 function in the lens fiber cell.
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