Nerve Growth Factor

NGF was discovered in the mouse submaxillary gland. It has a molecular weight of 13,259 and exists in a complex of 140 kDa. The complex contains two molecules of NGF (/3-subunits) together with two a-and two y-subunits (the y-subunit is arginine esterase). Apparently the identity of the a-subunits remains unclear. Although NGF is not a mitogen, it prevents apop-tosis of neurons. A now classical demonstration of the induction of apoptosis is the withdrawal of NGF, usually in chick embryos, that triggers programmed cell death. This is the case during development, but dependence on NGF for neuronal survival does not occur in the adult. NGF causes a rat pheochromocytoma, PC-12, to differentiate into sympathetic neurons. Experimentally, NGF can also act as a chemoattractant for neutrophilic leukocytes. The structure of the complex containing NGF is shown in Figure 19-11.

Other growth factors with homology to NGF do exist. Examples of these are neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF). Two other factors fall into this class of NGF homologues, but they have not been well described. Ciliary neurotrophic factor (CNTF) is a survival factor for chick ciliary ganglia parasympathetic neurons; however, it is different from neurotrophins NT-3 and BDNF. CNTF is expressed throughout the central nervous system and the peripheral nervous system and is a survival factor for neurons in these regions at various developmental stages. It is

Growth Hormone And Ngf

figure 19-8 Crystal structure of TGF-ft (A) Topology diagram of a TGF-/32 subunit. The a-helices are labeled as ay a2, and a3, and peptide strands in ftsheets are labeled from ft through ft. The residues involved in the regular secondary structure are as follows: <*,, residues 4-8; a^ 24-28; a3, 58-68; ft, 15-18; ft, 20-23; ft, 37-40; ft, 42-46; ft, 77-80; ft, 82-91; ft, 96-102; ft, 104-106; and ft, 109-112. (B) Schematic drawing of the primary and secondary structure of a TGF-/32 subunit. Hydrogen bonds in the ftstrands and loops are indicated by dashed lines. The analogy to a left hand can be seen. The heel (helix a3) is to the right and the fingers (ftstrands) are to the left with the third and fourth fingers twisted. Reproduced with permission from Daopin, A., Piez, K. A., Ogawa, Y., and Davies, D. R. (1992). Crystal structure of transforming growth factor-ft2: An unusual fold for the superfamily. Science 257, 369-373.

figure 19-8 Crystal structure of TGF-ft (A) Topology diagram of a TGF-/32 subunit. The a-helices are labeled as ay a2, and a3, and peptide strands in ftsheets are labeled from ft through ft. The residues involved in the regular secondary structure are as follows: <*,, residues 4-8; a^ 24-28; a3, 58-68; ft, 15-18; ft, 20-23; ft, 37-40; ft, 42-46; ft, 77-80; ft, 82-91; ft, 96-102; ft, 104-106; and ft, 109-112. (B) Schematic drawing of the primary and secondary structure of a TGF-/32 subunit. Hydrogen bonds in the ftstrands and loops are indicated by dashed lines. The analogy to a left hand can be seen. The heel (helix a3) is to the right and the fingers (ftstrands) are to the left with the third and fourth fingers twisted. Reproduced with permission from Daopin, A., Piez, K. A., Ogawa, Y., and Davies, D. R. (1992). Crystal structure of transforming growth factor-ft2: An unusual fold for the superfamily. Science 257, 369-373.

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