Avidin is a
66-KDa glycoprotein synthesized in the oviduct of a hen and deposited in
the albumen of its eggs. It binds the water-soluble vitamin biotin
(vitamin B7 or H) very tightly – irreversibly – and specifically, with
an outstanding dissociation constant of ~10-15 M. The protein, its
stability and affinity for biotin, have been extensively investigated
and characterized. It folds into a quaternary tetramer structure made of
4 subunits of identical amino acid composition and sequence, each
containing 9 lysine residues.
Avidin is highly
cationic with an isoelectric point (pI) of about 10.5. Glycosylation
occurs at the Asn-17 residue, in a typical NXT(S) or Asn-Xxx-Thr(Ser)
type carbohydrate-containing consensus sequence. Oligosaccharide
components (heterogeneous structures composed largely of mannose (Man)
and N-acetylglucosamine (GlcNac)) and positively charged amino acid
residues (Lys & Arg) can interact nonspecifically with lectins and
negatively charged cell surfaces and nucleic acids, thereby potentially
causing nonspecific bindings in diagnostic and therapeutic
applications1. Bioengineering methods have been developed to suppress
such nonspecific bindings. The result:
NeutraLite Avidin,
a nonspecific binding-free form of native avidin, in which the
signal/background ratio can be customarily adjusted (see NeutraLite
Oligomers) and the biotin-specific binding can be made reversible (see
Nitroavidin, Avidin Monomer, Iminobiotin) to accommodate an ever larger range of applications.
Sugar heterogeneity of
avidin. Comparison of glycopeptides from
ovalbumin and avidin shows that the avidin carbohydrate contains at
least three distinct oligosaccharide structural types of similar size as
shown above; N-linked glycan at Asn-17 consists of
GlcNAc(beta1-2)Man(alpha1-3)[GlcNAc(beta1-4)][Man(alpha1-?)Man(alpha1-6)]Man(beta1-4)GlcNAc(beta1-4)GlcNAc.
Some terminal galactose may even be present on some glycans.
Avidin |
Avidin biotin |
Native Avidin |
Nitrolite Avidin
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