Sequential pH-driven dimerization and stabilization of the N-terminal domain enables rapid spider silk formation.

Kronqvist N, Otikovs M, Chmyrov V, Chen G, Andersson M, Nordling K, Landreh M, Sarr M, J├Ârnvall H, Wennmalm S, Widengren J, Meng Q, Rising A, Otzen D, Knight SD, Jaudzems K, Johansson J

Nat Commun 5 (-) 3254 [2014-02-11; online 2014-02-11]

The mechanisms controlling the conversion of spider silk proteins into insoluble fibres, which happens in a fraction of a second and in a defined region of the silk glands, are still unresolved. The N-terminal domain changes conformation and forms a homodimer when pH is lowered from 7 to 6; however, the molecular details still remain to be determined. Here we investigate site-directed mutants of the N-terminal domain from Euprosthenops australis major ampullate spidroin 1 and find that the charged residues D40, R60 and K65 mediate intersubunit electrostatic interactions. Protonation of E79 and E119 is required for structural conversions of the subunits into a dimer conformation, and subsequent protonation of E84 around pH 5.7 leads to the formation of a fully stable dimer. These residues are highly conserved, indicating that the now proposed three-step mechanism prevents premature aggregation of spidroins and enables fast formation of spider silk fibres in general.

Fluorescence Correlation Spectroscopy [Collaborative]

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PubMed 24510122

DOI 10.1038/ncomms4254

Crossref 10.1038/ncomms4254

ncomms4254