Model peptide studies of sequence repeats derived from the intracrystalline biomineralization protein, SM50. II. Pro,Asn-rich tandem repeats.
In the biomineralization process, a number of Pro-rich proteins participate in the formation of three-dimensional supramolecular structures. One such protein superfamily, the Pro,Gly-rich sea urchin intracrystalline spicule matrix proteins, form protein-protein supramolecular assemblies that modify the microstructure of the inorganic mineral phase (calcite) within embryonic sea urchin spicules and adult sea urchin spines. These proteins represent a useful model for understanding Pro sequence usage and the resulting generation of extended or "open" structures for protein-protein and/or protein-crystal recognition. In the sea urchin spicule matrix protein, SM50 (Strongylocentrotus purpuratus), there exists an unusual 20-residue Pro,Asn-containing repeat, &bond;PNNPNNPNPNNPNNPNNPNPbond which links the upstream 15-residue C-terminal domain and the downstream 211-residue beta-spiral repeat domain. To define the structural preferences of this 20-residue repeat, we created a 20-residue N- and C-terminal "capped" peptidomimetic of this sequence. Using far-uv CD dichroism, CH(alpha) and alpha-(15)N conformational shifts, (3)J(NH-CHalpha) coupling constants, sequential d(NN(i, i + 1)) rotating frame nuclear Overhauser effect connectivities, d(alphaN(i, i + 1))/d(NN(i, i + 1)) intensity ratios, amide temperature shift coefficients, amide solvent exchange, and simulated annealing refinement protocols, we have determined that this 20-residue repeat motif adopts an extended "twist" structure consisting of turn- and coil-like regions. These findings are consistent with previous studies, which have shown that Pro-rich tandem repeats adopt extended, flexible structures in solution. We hypothesize that this 20-residue repeat may fulfill the role of a mineral-binding domain, a protein-protein docking domain, or as an internal "molecular spacer" for the SM50 protein during spicule biocomposite formation.
Zhang
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B
Laboratory for Chemical Physics, New York University, 345 E. 24th Street, New York, NY 10010, USA.
Xu
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Evans
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JS
D020816:Amino Acid Motifs; D000818:Animals; D002942:Circular Dichroism; D003198:Computer Simulation; D003598:Cytoskeletal Proteins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D012617:Sea Urchins
D003598:Cytoskeletal Proteins; D009842:Oligopeptides