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Nat Commun. 2014;5:3254. doi: 10.1038/ncomms4254.

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

Author information

1
KI Alzheimer Disease Research Centre, NVS Department, Karolinska Institutet, Novum, 5th floor, SE-141 86 Stockholm, Sweden.
2
Department of Physical Organic Chemistry, Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga LV-1006, Latvia.
3
Experimental Biomolecular Physics, Royal Institute of Technology-KTH, Albanova, SE-106 91 Stockholm, Sweden.
4
Institute of Biological Sciences and Biotechnology, Donghua University, Shanghai CN-201620, China.
5
Department of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences, The Biomedical Centre, SE-751 23 Uppsala, Sweden.
6
Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
7
1] Experimental Biomolecular Physics, Royal Institute of Technology-KTH, Albanova, SE-106 91 Stockholm, Sweden [2] Science for Life Laboratory, SE-171 65 Solna, Sweden.
8
1] KI Alzheimer Disease Research Centre, NVS Department, Karolinska Institutet, Novum, 5th floor, SE-141 86 Stockholm, Sweden [2] Department of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences, The Biomedical Centre, SE-751 23 Uppsala, Sweden.
9
Center for Insoluble Protein Structures (inSPIN), iNANO and Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark.
10
Department of Cell and Molecular Biology, Uppsala University, SE-751 24 Uppsala, Sweden.
11
1] KI Alzheimer Disease Research Centre, NVS Department, Karolinska Institutet, Novum, 5th floor, SE-141 86 Stockholm, Sweden [2] Department of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences, The Biomedical Centre, SE-751 23 Uppsala, Sweden [3] Institute of Mathematics and Natural Sciences, Tallinn University, Narva mnt 25, EE-101 20 Tallinn, Estonia.

Abstract

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.

PMID:
24510122
DOI:
10.1038/ncomms4254
[Indexed for MEDLINE]
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