NGF-beta family

General Activity
Nerve growth factor (NGF) is a vertebrate protein that stimulates the differentiation and maintenance of neurons in the central and peripheral nervous system (Cohen et al., 1957 ). Other physiological functions have also been described, such as regulation of esterase activity (Palmer and Neet, 1980, Rao and Neet, 1984 ), regulation of inflammation (Villoslada and Genain, 2004, Freund-Michel and Frossard, 2008 ) and wound healing (Kawamoto and Matsuda, 2004 ).

The reason why NGF is a significant component in a large variety of Elapidae and Viperidae snake venoms (Kashima et al, 2002 ) and its role in envenomation are not clear. Recent studies on the NGFs isolated from Naja kaouthia suggest that they act as metalloprotease inhibitors to prevent metalloprotease autodigestion and/or protection against prey proteases (Wijeyewickrema et al., 2010 ).

Structure
Venom NGFs are non-covalently linked dimers that are either glycosylated (with apparent molecular masses of 17-20 kDa), or not glycosylated (with molecular masses of 12-13 kDa) (Trummal et al., 2011 ).