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The excised heat-shock domain of alphaB crystallin is a folded, proteolytically susceptible trimer with significant surface hydrophobicity and a tendency to self-aggregate upon heating.

DIR@IMTECH: CSIR-Institute of Microbial Technology

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Title The excised heat-shock domain of alphaB crystallin is a folded, proteolytically susceptible trimer with significant surface hydrophobicity and a tendency to self-aggregate upon heating.
 
Creator Kundu, Bishwajit
Shukla, Anshuman
Chaba, Rachna
Guptasarma, Purnananda
 
Subject QR Microbiology
 
Description The lens protein, alpha-crystallin, is a molecular chaperone that prevents the thermal aggregation of other proteins. The C-terminal domain of this protein (homologous to domains present in small heat-shock proteins) is implicated in chaperone function, although the domain itself has been reported to show no chaperone activity. Here, we show that the domain can be excised out of the intact alphaB polypeptide and recovered directly in pure form through the transfer of CNBr digests of whole lens homogenates into urea-containing buffer, followed by dialysis-based refolding of digests under acidic conditions and a single gel-filtration purification step. The folded (beta sheet) domain thus obtained is found to be (a) predominantly trimeric, and to display (b) significant surface hydrophobicity, (c) a marked tendency to undergo degradation, and (d) a tendency to aggregate upon heating, and on exposure to UV light. Thus, the twin 'chaperone' features of multimericity and surface hydrophobicity are clearly seen to be insufficient for this domain to function as a chaperone. Since alpha-crystallin interacts with its substrates through hydrophobic interactions, the hydrophobicity of the excised domain indicates that separation of domains may regulate function; at the same time, the fact is also highlighted that surface hydrophobicity is a liability in a chaperone since heating strengthens hydrophobic interactions and can potentially promote self-aggregation. Thus, it would appear that the role of the N-terminal domain in alpha-crystallin is to facilitate the creation of a porous, hollow structural framework of >/=24 subunits in which solubility is effected through increase in the ratio of exposed surface area to buried volume. Trimers of interacting C-terminal domains anchored to this superstructure, and positioned within its interior, might allow hydrophobic surfaces to remain accessible to substrates without compromising solubility.
 
Publisher Elsevier Science
 
Date 2004-08
 
Type Article
PeerReviewed
 
Format application/pdf
 
Identifier http://crdd.osdd.net/open/205/1/guptasarma2004.1.pdf
Kundu, Bishwajit and Shukla, Anshuman and Chaba, Rachna and Guptasarma, Purnananda (2004) The excised heat-shock domain of alphaB crystallin is a folded, proteolytically susceptible trimer with significant surface hydrophobicity and a tendency to self-aggregate upon heating. Protein expression and purification, 36 (2). pp. 263-71. ISSN 1046-5928
 
Relation http://www.sciencedirect.com/science/article/pii/S1046592804001147
http://crdd.osdd.net/open/205/