Synthetic biology, bioinformatics and nanotechnologies Lectures L3.1 Structural investigation of mammalian serum albumins

Serum albumins appeared in early vertebrates as a result of gene triplication. Their canonical structure supported by a conservative set of disulfide bridges is maintained in all mammals, but the changes in sequence are highly correlated with the evolution of each species. Serum albumin is the main carrier for metabolites, hormones and drugs in the blood. It collects drugs from the place of application and hormones from the secretion sites, then delivers them to other parts of the body. To be able to bind a variety of ligands possessing different chemical properties, albumin developed a number of binding sites, among them: eleven for fatty acids, two primary ones for drugs, one for bilirubin and heme in primates and a number of sites selective for binding other ligands. The changes in protein sequence adjusted the shape and charge distribution of binding pockets and modulated the affinity of serum albumin to specific ligands. Until now, the structural investigation of mammalian serum albumins, probably due to crystallization and cryoprotection problems, has been concentrated only on human serum albumin. We are breaking this impasse and presenting crystal structures of a number of mammalian serum albumins in apo forms and in complexes with ligands. Bovine serum albumin (BSA), one of the most popular proteins in laboratory practice, used in many experiments as an HSA model, has only 79% of sequence identity to HSA and its crystal structure is currently being determined by us to 2.47Å. We have solved crystal structures of horse and rabbit serum albumins at resolutions 2.01 – 2.67Å and have collected diffraction data from crystals of goat and porcine serum albumins. The knowledge of BSA and other mammalian serum albumin crystal structures will allow direct structural comparison and evaluation of ligand binding properties in relation to HSA, for which we have found our own crystallization conditions and determined its crystal structure. Comparison of the crystal structures of investigated serum albumins can highlight the differences resulting from sequence and spatial specificity. BSA is used in many fluorescent tests, but no one has structurally determined in which places the ligands interact with this protein. The apo structures of other mammalian serum albumins will show in which experiments these proteins can be effectively utilized as a replacements for HSA. Acknowledgements Project supported by Grant NN405 363939 from Polish Ministry of Science and Higher Education. L3.2