Small heat shock proteins (sHSPs) as potential drug targets.

Small heat shock proteins (sHSPs) belong to a family of 12- to 43-kDa proteins that are ubiquitous and are largely conserved in amino acid sequence among all organisms. The principal heat-shock proteins that have chaperone activity (that is, they protect newly made proteins from misfolding) belong to five conserved classes: HSP100, HSP90, HSP70, HSP60 and the small heat-shock proteins (sHSPs). The sHSPs (which include alpha crystallin) can form large multimeric structures and have a wide range of cellular functions, including endowing cells with thermotolerance in vivo and being able to act as molecular chaperones in vitro; sHSPs do this by forming stable complexes with folding -or unfolding--intermediates of their protein substrates, probably the molten globule. This paper includes: a brief survey of the chaperone family, the small heat shock protein superfamily, transcription of sHSPs, sequence comparisons and structural models of small heat shock proteins--structural elements as potential drug targets, sHSPs as chaperone-like proteins, alpha crystallin chaperone-like activity, conformational diseases--the role of alpha crystallin small heat shock protein superfamily proteins, post-translational modification and useful pharmacological agents. Functionality of small heat shock proteins--targets and diseases where pharmacologically active agents are of importance, alpha crystallin--small heat shock proteins and prion diseases: specific targets for diagnostic tests and drug development, details of some specific small heat shock proteins as drug targets, structural and functional implications for treatment.

Chaperone function of mutant versions of alpha A- and alpha B-crystallin prepared to pinpoint chaperone binding sites.

A major stress protein, alpha-crystallin, functions as a chaperone. Site-directed mutagenesis has been used to identify regions of the protein necessary for chaperone function. In this work we have taken some of the previously described mutants produced and assessed their chaperone function by both a traditional heat-induced aggregation method at elevated temperature and using enzyme methods at 37 degrees C. In general the different assays gave parallel results indicating that the same property is being measured. Discrepancies were explicable by the heat lability of some mutants. Most mutants had full chaperone function showing the robust nature of alpha-crystallin. A mutant corresponding to a minor component of rodent alpha A-crystallin, alpha Ains-crystallin, had decreased chaperone function. Decreased chaperone function was also found for human Ser139--> Arg, Thr144-->Arg, Ser59-->Ala mutants of alpha B-crystallin and double mutants Ser45-->Ala/Ser59-->Ala, Lys103--> Leu/His104-->Ile, and Glu110-->His/His111-->Glu. A mutant Phe27-->Arg that was the subject of previous controversy was shown to be fully active at physiological temperatures.

Maintenance of chaperone-like activity despite mutations in a conserved region of murine lens alphaB crystallin.

PURPOSE: To understand the relationship between certain conserved residues in alphaB crystallin and the chaperone-like function of the protein. METHODS: In alphaB crystallin, residues H101 to R120 are highly conserved between alphaB crystallin and alphaA crystallin (85% identity), and between alphaB crystallin and the small heat shock protein hsp 27 (80% identity). We made three substitution mutants of alphaB crystallin: the single mutant F118A, and the double mutants K103L/H104I, and E110H/H111E. RESULTS: Polyacrylamide gel electrophoresis revealed no decrease in aggregate size or measureable structural changes between them and the native structure. Using the insulin aggregation assay, all three mutants had identical chaperone-like activity to the wild-type recombinant alphaB crystallin. CONCLUSIONS: Despite the high conservation in this area of sequence between alphaB crystallin, alphaA crystallin, and the small heat shock protein hsp 27, mutations F118A, K103L/H104I, and E110H/H111E did not significantly alter chaperone-like activity.

Effect of mutations of murine lens alphaB crystallin on transfected neural cell viability and cellular translocation in response to stress.

We examined the influence of over-expressed native and mutant murine lens alphaB crystallin on the response of a murine neural cell line to heat and ionic strength shock. Native and mutant (F27R and KK174/175LL) murine alphaB crystallin amplicons were subcloned into a Lac-Switch IPTG-inducible RSV promoter eukaryotic vector, and transfected into N1E-115 cells using lipofectin. Expression was induced maximally 8 h after addition of IPTG (optimal final concentration 1 mM) to the medium. Cells grew normally after transfection with native and mutant murine alphaB crystallin. We demonstrated expression of the protein using specific anti-alpha crystallin antibodies. Viability under severe heat and ionic strength stress increased when cells had been transfected with native alphaB crystallin, but not with mutants F27R or KK174/175LL. Heat shock caused translocation of both native and mutant alphaB crystallins into the central region of the cells. These results show that mutations in alphaB crystallin that effect its chaperone-like activity may also influence viability of N1E-115 neural cells under stress, while not influencing the distribution of the protein within the cell.