The structural biology of growth factor receptor activation.
ABSTRACT Stimulation of cells by growth factors triggers cascades of signalling that result in cellular responses such as growth, differentiation, migration and survival. Many growth factors signal through receptor tyrosine kinases, leading to dimerization, trans-phosphorylation and activation of tyrosine kinases that phosphorylate components further downstream of the signal transduction cascade. Using insulin-like growth factor, nerve growth factor, hepatocyte growth factor and fibroblast growth factor as examples, we show that the globular architecture of the growth factors is essential for receptor binding. We describe how nerve growth factor (NGF) is a symmetrical dimer that binds four storage proteins (two alpha-NGF and two gamma-NGF) to give a symmetrical hetero-hexameric 7SNGF organised around the beta-NGF dimer. It binds the extracellular domains of two receptor molecules in a similar way, so dimerising the receptor. Hepatocyte growth factor/scatter factor (HGF/SF) probably binds its receptor as a dimer stabilised by interactions with heparan sulfate, and fibroblast growth factor (FGF) binds its receptor as a dimer cross-linked by heparan sulfate. Surprisingly, insulin and insulin-like growth factor (IGF) bind in the monomeric form to receptors that are already covalent dimers. We propose that, in general, weak binary interactions between growth factor and individual domains of receptors are enhanced by cooperative interactions with further receptor domains, and sometimes other components like heparan, to give rise to specific multi-protein/domain complexes.
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ABSTRACT: PURPOSE: Cataract surgery is blighted by posterior capsule opacification (PCO). Our aim was to understand the biological basis for age-related differences in PCO/wound healing rates. METHODS: Human capsular bags were prepared by sham cataract surgery on donor lenses. FGF and HGF levels were determined using ELISA. Protein synthesis rates were elucidated by 35S-methionine incorporation. U0126, SB203580 and SP600125 were used to disrupt ERK, p38 and JNK mediated signaling respectively. Level of total and phospho ERK, c-jun, P38 and JNK plus cytokines were detected using a BIOPLEX array system. RESULTS: Following a 2-day culture period, significant decreases in IL-1β and IL-6 and increases in IL-10, IL-12, IL-13 and VEGF in the >60 years group were observed compared to < 40 years group. Capsular bags from aged donors contained ≥ levels of HGF and FGF than younger counterparts and had greater rates of protein synthesis. Inhibition of ERK, p38 and JNK signaling significantly suppressed cell coverage on the posterior capsule. pERK, p-c-jun, pP38 and pJNK were consistently lower in aged cell populations; total signaling protein expression was unaffected by age. Serum stimulation increased pERK, p-c-jun, and pJNK levels in cells of all ages and p38 in the aged group only. CONCLUSIONS: Ligand availability to cells is not a limiting factor as we age, but the ability to convert this resource into signaling activity is. We therefore propose that overall signaling efficiency is reduced as a function of age, which consequently limits wound-healing response rates after injury.Investigative ophthalmology & visual science 12/2012; · 3.43 Impact Factor
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ABSTRACT: The vast number of candidate proteins generated from genome projects are creating enormous opportunities for biologists. However, efficient expression of genes in homologous/heterologous expression systems and rapid purification steps are actually major bottlenecks. In fact, although many recombinant proteins have been successfully produced from common prokaryotic (Escherichia coli) and eukaryotic (yeast and CHO cells) hosts, these conventional systems have often proved to be unproductive due to the peculiar properties of the protein to be produced. Indeed, beside the obvious impossibility of achieving a large scale production of thermally labile proteins at the normal E. coli growth temperature, degradation of the product by the host proteases and the incorrect folding of the nascent polypeptides, resulting in the proteins aggregation and accumulation as insoluble inclusion bodies, are sometimes observed (Speed et al. 1996).12/2007: pages 365-379;
- Studies in Surface Science and Catalysis - STUD SURF SCI CATAL. 01/2001; 135:345-345.