monovalent streptavidin

[R Hanemaaijer]

Hi netters,

Avidin or streptavidin have a high affinity for biotin. A mature 
(strept)avidin molecule is multivalent, since it has four biotin 
binding sites. 
We are looking for monovalent streptavidin. Does anybody know if 
there's a company that sells such a molecule. A second question 
is: Does anybody know if mono- or multivalent streptavidin can be 
or has been produced in prokaryotic or eukaryotic expression systems?
We assume that only a few amino acid residues are essential for 
multimerization of avidin core units. Is known whether mutations of 
some amino acid residues will disrupt tetramer formation without 
affecting biotin binding.
Thanks,

Roeland Hanemaaijer
Gaubius Lab, Leiden, NL 
E-mail: R.Hanemaaijer at PG.TNO.NL