Model peptide studies of sequence repeats derived from the intracrystalline biomineralization protein, SM50. I. GVGGR and GMGGQ repeats

We report solution-state pulsed field gradient nmr studies of a native sequ ence-derived 23-residue peptidomimetic, N-alpha-acetyl-QPGVGGRQPGMGGQPGVGGR QPG-C-alpha-amide, that incorporates the prevalent GVGGR and GMGGQ repeats found in the sea urchin embryo intracrystalline spicule matrix protein, SM5 0 (Strongylocentrotus purpuratus). These repeats are sequence homologues of elastin protein repeats (VPGVG, VGGVG, and APGVGV) and spider dragline sil k protein repeats (GPGG, GQGG, and QPGYG). Using rotating frame nuclear Ove rhauser effect (ROE) connectivities, CHalpha proton conformational shifts, (3)J(NH-CH alpha) coupling constants, amide temperature shift coefficients, and pulsed field gradient ROE spectroscopy solvent exchange measurements, we find that the 23-mer peptidomimetic possesses a multiple beta-turn struc ture in aqueous solution, in equilibria with an extended or coil structure (60% beta-turn: 40% random coil). The GVGGR sequence adopts a double p-rum conformation thai is stabilized by two hydrogen bonds (R7 --> V4, R20 --> V 17; G6 --> G3, G19 --> G16). The GMGGQ region adopts a single beta-turn con formation that is stabilized by a hydrogen bond involving residues Q14 and Mil. Repenting beta-turn structures, or beta-spirals, mar play an important Pole with regard to matrix assembly, protein stability, molecular elastici ty, and/or protein-crystal recognition within the spicule mineralized matri x. (C) 1999 John Wiley & Sons, Inc.