Anomalies in the ionic properties of serum albumin.
The documented difference in the isoionic points of native and unfolded serum albumins is revisited with computational methods. Good agreement between calculated and measured DeltapIs is found, with the molecular origin appearing to reside in a diverse set of carboxyl group titrations. Although histidine ionization plays only a minor role in bringing about the DeltapI, the identification of three histidine residues with low computed pK(a)s (around pH 5) suggests an explanation for the mismatch between experimentally derived group pK(a)s and the pI of the native protein. Computed electrostatic properties (including pI) of native serum albumins are compared with a set of 178 nonenzyme proteins. We find that the degree of interdigitation of positive and negative charges is extreme for serum albumin, and discuss the relationship to protein solubility and pH-dependent structural transitions.
Salaman
Myer R
MR
Department of Immunology, Imperial College School of Medicine, St. Mary's Campus, Norfolk Place, London W2 1PG, UK.
Warwicker
Jim
J
D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D007526:Isoelectric Point; D011487:Protein Conformation; D012709:Serum Albumin / Q000737:chemistry*; D012710:Serum Albumin, Bovine / Q000737:chemistry; D055672:Static Electricity; D017186:Titrimetry
D007477:Ions; D012709:Serum Albumin; D012710:Serum Albumin, Bovine