Protein-Protein Interactions Between Acidic and Basic ß-crystallins

Abstract

Purpose:: To investigated protein-protein interactions between acidic and basic ß-crystallins.

Methods:: A mammalian two-hybrid system was used to detect protein-protein interactions between acidic (ßA1, ßA2, ßA3) and basic (ßB1, ßB2, ßB3) ß-crystallins. Various ß-crystallin genes were cloned to the two-hybrid system vectors pM (prey protein) and pVP16 (bait protein). These two genes along with a reporter gene pG5SEAP were co-transfected to HeLa cells. After culture, secreted alkaline phosphatase (SEAP) activities were determined by reading fluorescence at 360/449 nm. Many ß-crystallins were expressed and studied with some physicochemical methods.

Results:: The results indicate that all acidic-basic (ßA-ßB) pairs show strong interactions. For acidic pairs or basic pairs, only three pairs (ßA1-ßA1, ßA3-ßA3, ßA1-ßA3) show strong interactions. ßA2-ßA2 shows very low activity. Protein expression experiments show that ßA2-crystallin has very low solubility and confocal fluorescence microscope cell imaging shows a lot of inclusions for GFP-ßA2 fusion protein.

Conclusions:: Our results demonstrated interactions among dimeric ß-crystallins through either subunit exchange or charge and hydrophobic interactions. The strong interactions between the lowly soluble ßA2-crystallin and basic ßB1-crystallin indicates that interactions enhance the solubility. The observed interactions may be responsible in the oligomerization of ß-crystallins in the lens.

Keywords: crystallins • protein structure/function • proteomics