C-terminal lysine truncation increases thermostability and enhances chaperone-like function of porcine alphaB-crystallin.
The carboxyl-terminal segment of alpha-crystallin, a major lens protein of all vertebrates, has a short and flexible peptide extension of about 20 amino acid residues that are very susceptible to proteolytic truncation and modifications under physiological conditions. To investigate its role in crystallin aggregation and chaperone-like activity, we constructed a mutant of porcine alphaB-crystallin with C-terminal lysine truncated end, which unexpectedly showed better chaperone-like function than wild-type alphaB-crystallin. From circular dichroism (CD) spectra, we show that the mutant possesses similar secondary and tertiary structures to those of native purified and recombinant alphaB-crystallins. Analytical ultracentrifugation revealed that the truncated mutant was smaller than wild-type alphaB-crystallin in aggregation size and mass. The observed higher thermostability and anti-thermal aggregation propensity of the truncated alphaB-crystallin mutant than wild-type alphaB-crystallin are in contrast to the prevailing notion that mutations at the C-terminal lysines of alphaB-crystallin result in substantial loss of chaperone-like activity, despite the overall preservation of secondary structure. The detailed characterization of the C-terminal deletion mutants may provide some deeper insight into the chaperoning mechanism of the structurally related small heat-shock protein family.
Liao
Jiahn-Haur
JH
Institute of Biochemical Sciences, National Taiwan University, Taipei 10617, Taiwan.
Lee
Jiahn-Shing
JS
Chiou
Shyh-Horng
SH
D000818:Animals; D002942:Circular Dichroism; D003459:Crystallins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000378:metabolism*; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D009154:Mutation; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013552:Swine; D013696:Temperature
D003459:Crystallins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D008239:Lysine