Nerve growth factor (NGF or β-NGF) is a vertebrate protein that stimulates division and differentiation of sympathetic and embryonic sensory neurons [1,2]. NGF is a protein of about 120 residues that is cleaved from a larger precursor molecule. It contains six cysteines all involved in intrachain disulfide bonds. A schematic representation of the structure of NGF is shown below:

                                    +------------------------+
                                    |                        |
                                    |    *******             |
        xxxxxxCxxxxxxxxxxxxxxxxxxxxxCxxxxCxxxxxCxxxxxxxxxxxxxCxCxxxx
              |                          |     |               |
              +--------------------------|-----+               |
                                         +---------------------+

'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.

Some proteins have been found [3] to be structurally and functionally related to NGF, these are:

• Brain-derived neurotrophic factor (BDNF), a protein that promotes the survival of neuronal populations all located either in the central nervous system or directly connected to it.
• Neurotrophin-3 (NT-3), a protein that seems to promote the survival of visceral and proprioceptive sensory neurons.
• Neurotrophins-4/5 (NT-4/5), which elicit neurite outgrowth from explanted dorsal root ganglia and could play a role in oogenesis and/or early embryogenesis.
• Neurotrophin-6.
• Neurotrophin-7 from zebrafish.

The pattern we have developed for the NGF family spans the central region of these proteins and include two of the six cysteines involved in disulfide bonds.