Martins Otikovs, Department of Physical Organic Chemistry, Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga , Letland
Volodymyr Chmyrov, Royal Institute of Technology, Sverige
Gefei Chen, Institute of Biological Sciences and Biotechnology, Donghua University, Shanghai CN-201620, Kina
Marlene Andersson, Swedish University of Agricultural Sciences, Sverige
Kerstin Nordling, Karolinska Institutet, Sverige
Michael Landreh, Karolinska Institutet, Sverige
Médoune Sarr, Karolinska Institutet, Sverige
Hans Jörnvall, Karolinska Institutet, Sverige
Stefan Wennmalm, 1] Experimental Biomolecular Physics, Royal Institute of Technology-KTH, Albanova, SE-106 91 Stockholm, Sweden [2] Science for Life Laboratory, SE-171 65 Solna, Sverige
Jerker Widengren, Royal Institute of Technology, Sverige
Qing Meng, Institute of Biological Sciences and Biotechnology, Donghua University, Shanghai CN-201620, Kina
Anna Rising, 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, Sverige
Kristaps Jaudzems, Department of Physical Organic Chemistry, Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga LV-1006, Letland
Jan Johansson, 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, Estland
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.