Protective proteins, functions

Jung H, Toth PT, White PA, Miller RJ (2008) Monocyte chemoattractant protein-1 functions as a neuromodulator in dorsal root ganglia neurons. J Neurochem 104 254-263 Kahn L, Alonso G, Normand E, Manzoni OJ (2005) Repeated morphine treatment alters polysia-lylated neural cell adhesion molecule, glutamate decarboxylase-67 expression and ceU proliferation in the adult rat hippocampus. Em J Nemosci 21 493-500 Kaul M, Ma Q, Medders KE, Desai MK, Lipton SA (2007) HIV-1 coreceptors CCR5 and CXCR4 both mediate neuronal cell death but CCR5 paradoxically can also contribute to protection. Cell Death Differ (2) 296-305... 

Although equal amounts of the two possible forms are generated in every synthesis of amino acids, (almost) only L-amino acids are incorporated into proteins and peptides. This phenomenon is valid for the amino acids in all life forms, from the bacterium to the elephant. But there are exceptions some antibiotics contain D-amino acids in their proteins, and these also occur in a few components of cell walls. Here, the D-amino acids have a certain protecting function with respect to degradation enzymes, which are specialised to deal with L-amino acids. 

The response of cells to stress (including ROS and reactive metabolites) includes the upregulation of synthesis of stress proteins, which play a role in cell survival and thus serve a protective function. These are at a low level in the normal cell but help to maintain cell homeostasis. 

These proteins are important for binding potentially toxic metals such as cadmium, mercury, and lead, which all bind to sulfydryl groups. Consequently, the binding and removal of these metals are protective functions. Metallothioneins are markedly induced by cadmium exposure and the small protein, rich in SH groups, can then sequester the metal. They also may have a protective role in oxidative stress and protect redox-sensitive processes. The protein also has a role in cadmium nephrotoxicity (see chap. 7). 

Figure 7.21 The cascade of events in the liver following a toxic dose of paracetamol. Hsp10, Hsp 60 are heat shock proteins, which have a protective function, cyt c is ctyochrome c. TNF-a, EGR-1, and GM-CSF are all genes involved with apoptosis, c-fos, APAF-1, and c-myc are also genes.

Hsp 10 and Hsp 60 are chaperone proteins located in the mitochondria, which have a protective function but are released when the mitochondria are damaged, hence the mitochondrial level drops after paracetamol. 

Immunoglobulins, oq-trypsin inhibitor and a2-macroglobulin,k ten or more blood clotting factors and proteins of the complement system all have protective functions that are discussed elsewhere in this book. Hormones, many of them proteins, are present in the blood as they are carried to their target tissues. Many serum proteins have unknown or poorly understood functions. Among these are the acute phase proteins, whose concentrations rise in response to inflammation or other injury. 

An example is adrenodoxin reductase (see chapter banner, p. 764), which passes electrons from NADPH to cytochrome P450 via the small redox protein adrenodoxin. This system functions in steroid biosynthesis as is indicated in Fig. 22-7.209a b Other flavin-dependent reductases have protective functions catalyzing the reduction of ascorbic acid radicals,210 211 toxic quinones,212-214 and peroxides.215-218... 

Hamosh, M. 1998. Protective function of proteins and lipids in human milk. Biol. Neonate 74, 163-176. 

Also prevalent in ALS are reactive astrocytes, which stain intensively for the intermediate filament, glial fibrillary acidic protein (GFAP). These reactive astrocytes, with a hypertrophied appearance, are present throughout areas of degeneration. Reactive astrocytes can have multiple roles including a neuro-protective function (Liberto et al., 2004). 

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