R-phycoerythrin from Gracilaria chilensis: Estability and interaction among subunits.

Numerous biological macromolecules are arranged in complex interaction syst ems, to perform their biological function. Phycobiliproteins, the main poly peptidic components of the phycobilisomes, are very good examples for expla ining these interactions because their light harvesting and conduction func tion depend strongly on the three dimensional arrangement of the complex. The functional unit of R-phycoerythrin from Gracilaria chilensis is (alpha beta)(6) and all the subunits require to be perfectly packed to perform the function. For this reason it was selected to study the rol of the differen t type of interactions in the stability of the protein. To distinguish the contribution of some of the different type of interactions, differential sp ectrocopy was used to follow the effect of temperature, ionic strength and presence of urea and the structural information was used to analyse the int eraction surfaces that are produced during the association. Our results suggest that (alpha beta) is the minimum specie detectable beca use its interaction surface presents an important hydrophobic component and because in this process, 9 new hydrogen bonds are formed, that contribute to the stability. The stabilization of (alpha beta)(6), requires the contri bution of all the subunits involved.