A PULSED-FIELD GRADIENT NMR-STUDY OF THE AGGREGATION AND HYDRATION OFPARVALBUMIN

Pulsed field gradient NMR is a convenient alternative to traditional m ethods for measuring diffusion of biological macromolecules. In the pr esent study, pulsed field gradient NMR was used to study the effects o f calcium binding and hydration on carp parvalbumin. Carp parvalbumin is known to undergo large changes in tertiary structure with calcium l oading. The diffusion coefficient is a sensitive guide to changes in m olecular shape and in the present study the large changes in tertiary structure were clearly reflected in the measured diffusion coefficient upon calcium loading. The (monomeric) calcium-loaded form had a diffu sion coefficient of 1.4 x 10(-10) m(2) s(-1) at 298 K, which conforms with the structure being a nearly spherical prolate ellipsoid from X-r ay studies. The calcium-free form had a significantly lower diffusion coefficient of 1.1 x 10(-10) m(2) s(-1). The simplest explanation cons istent with the change in diffusion coefficient is that the parvalbumi n molecules form dimers upon the removal of Ca2+ at the protein concen tration studied (I mM). (C) 1997 Elsevier Science B.V.