Abstract
Purpose: :
Our recent studies showed that a low molecular weight peptide βA3/A1102-117 (SD(N)AYHIERLMSFRPIC), present in aged and cataract lens increased the scattering of light by β- and γ-crystallins and alcohol dehydrogenase (ADH) and also reduced the chaperone-like activity of α-crystallin (Invest. Ophthalmol. Vis. Sci. 2006 47: E-Abstract 2009). The present study was carried out to identify the βA3/A1102-117 peptide (SDAYHIERLMSFRPIC) interacting sites in αB-crystallin.
Methods: :
SDAYHIERLMSFRPIC peptide was labeled with a photoactivable, heterotrifunctional cross-linker, sulfo-succinimidyl-2-[6-(biotinamido)-2-{p-azidobenzamido}-hexanoamido] ethyl-1-3 dithio propionate (sulfo-SBED) and incubated with αB-crystallin at 37° for two hours and subjected photolysis to facilitate transfer of the biotin label from the peptide to αB-crystallin. Label transfer was confirmed by western blot, and αB-crystallin was digested with trypsin. Tryptic peptides from αB-crystallin carrying the sulfo-SBED label were purified by avidin affinity chromatography and βA3/A1102-117 interacting sites in αB-crystallin were identified by matrix assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF MS) and nanospray QqTOF MS/MS.
Results: :
The mass spectrometry analysis showed that the cross-linker from βA3/A1102-117 peptide was transferred to αB-crystallin sequences LEKDR70-74, HFSPEELKVK83-92, VKVLGDVIEVHGK91-103, VLGDVIEVHGKHEER93-107, KYR121-123, KQVSGPER150-157, EEKPAVTAAPK164-174 and EEKPAVTAAPKK164-175. This suggests that αB-crystallin sequences 70-74, 83-107, 121-123 and 150-157 in the α-crystallin domain and 164-175 in C-terminal extension interact with βA3/A1102-117 peptide.
Conclusions: :
Binding of βA3/A1102-117 peptide to the chaperone site (αB- 73-92) and C-terminal extension (αB-162-175, believed to be involved in solubilization of substrate-chaperone complex), may explain its anti-chaperone action against αB-crystallin.
Keywords: crystallins • chaperones • protein structure/function