Figure 2

Conformational changes associated with variations in fatty acid content (a) Superposition of HSA-hemin-myristate (opaque) on defatted HSA (semi-transparent). (b) Superposition of HSA-hemin-myristate (opaque) on HSA-myristate (semi-transparent). HSA-hemin-myristate was prepared with a 4-fold molar excess of fatty acid whereas the HSA-myristate complex was prepared with a 12-fold molar excess [9] which saturates the binding sites. The colour scheme is the same as Figure 1. In each case the structures were superposed using the C_α atoms from domain II (residues 197–383). Arrows indicate the relative domain movements. (c) Close-up views of myristate binding site 2 which traverses the interface between domains I and II for HSA-hemin-myristate. Selected amino acid sidechains are shown coloured by atom type. The fatty acid is depicted in a space filling-representation. Only the first seven carbon atoms of the methylene tail for which there is clear electron density are shown; the remainder of the tail is disordered but presumable extends further upward. (d) A similar close-up view of the same site in the HSA-myristate structure [9]. In this case the site is occupied by two fatty acid molecules in a tail-to-tail configuration. The upper part of fatty acid site 2 is labelled 2'. The additional relative movement of the two domains at the higher fatty acid concentration is evident from the relative dispositions of R10 and D255, which interact across the top of the bound fatty acid.