Deletion of Specific Conserved Motifs from the N-Terminal Domain of αB-Crystallin Results in the Activation of Chaperone Functions

Smaller oligomeric chaperones of alpha-crystallins (alpha A- and alpha B-) have received increasing attention due to their improved therapeutic potential in preventing protein aggregating diseases. Our previous study suggested that deleting 54-61 residues from the N-terminal domain (NTD) of alpha B-crystallin (alpha B & UDelta;54-61) decreases the oligomer size and increases the chaperone function. Several studies have also suggested that NTD plays a significant role in protein oligomerization and chaperone function. The current study was undertaken to assess the effect of deleting conserved 21-28 residues from the activated alpha B & UDelta;54-61 (to get alpha B & UDelta;21-28, & UDelta;54-61) on the structure-function of recombinant alpha B & UDelta;21-28, & UDelta;54-61. The alpha B & UDelta;21-28, & UDelta;54-61 mutant shows an 80% reduction in oligomer size and 3- to 25-fold increases in chaperone activity against model substrates when compared to alpha B-WT. Additionally, the alpha B increment 21-28, increment 54-61 was found to prevent beta-amyloid (A beta(1-42)) fibril formation in vitro and suppressed A beta(1-42)-induced cytotoxicity in ARPE-19 cells in a more effective manner than seen with alpha B-WT or alpha B increment 54-61. Cytotoxicity and reactive oxygen species (ROS) detection studies with sodium iodate (SI) showed that the double mutant protein has higher anti-apoptotic and anti-oxidative activities than the wild-type or alpha B increment 54-61 in oxidatively stressed cells. Our study shows that the residues 21-28 and 54-61 in alpha B-crystallin contribute to the oligomerization and modulate chaperone function. The deletion of conserved 21-28 residues further potentiates the activated alpha B & UDelta;54-61. We propose that increased substrate affinity, altered subunit structure, and assembly leading to smaller oligomers could be the causative factors for the increased chaperone activity of alpha B & UDelta;21-28, & UDelta;54-61.

Automated summary

This study demonstrates that specific mutations at certain residue positions in the N-terminal domain of α B-crystallin can reduce oligomer size and enhance chaperone function, indicating the importance of these residues in oligomerization and chaperone activity.