p.E84Q/E292A/D349N/E358Q/E389Q/D390N Glu84Gln/Glu292Ala/Asp349Asn/Glu358Gln/Glu389Gln/Asp390Asn (p.E115Q/E323A/D380N/E389Q/E420Q/D421N Glu115Gln/Glu323Ala/Asp380Asn/Glu389Gln/Glu420Gln/Asp421Asn in primary sequence with 31 amino-acids signal peptide) Electrostatic attraction hypothesis no significant effect