Bacteria protein turnover

Thermococcus litoralis, Desulfurococcus sp., and T. maritima, all having optimum temperatures of 85°C, have been characterized (22). Proteasomes, intracellular protease heteromultimeric complexes, based on two types of subunits a and writh Mr approaching 1 MDa, are common to the archaea and typically exhibit several different proteolytic specificities (59). Their cellular function relates to the need for protein turnover, particularly under stress conditions. Although proteasomes are fovmd in all eukaryotes, all archaea and some bacteria, their composition can vary. For instance, the hyperthermophile Pyrococcus furiosus has a 20S proteasome formed by one a-protein and two j8-proteins this proteasome has different amounts of each 8-protein depending on assembly temperature (59). 

Proteasomes are multisubunit peptidases found in all eukaryotes and archaea and some bacteria. The 20 S proteasome is found only in actinomycetales. Prokaryotic 20 S proteasome cores are self-compartmentalized peptidases composed of 14 a-subunits and 14 P-subunits, with the N-terminal threonines of the P-subunits providing the protease activity. Core particles from archaea and bacteria are simpler structures with homoheptameric rings of catalytic P-subunits flanked by homoheptameric rings of a-subunits. In bacteria, proteasomes are evolved in protein turnover, but in archaea, their function is unknown. Proteasomes are threonine peptidases (Darwin 2009 Murata et al. 2009). 

In be complexes bci complexes of mitochondria and bacteria and b f complexes of chloroplasts), the catalytic domain of the Rieske protein corresponding to the isolated water-soluble fragments that have been crystallized is anchored to the rest of the complex (in particular, cytochrome b) by a long (37 residues in bovine heart bci complex) transmembrane helix acting as a membrane anchor (41, 42). The great length of the transmembrane helix is due to the fact that the helix stretches across the bci complex dimer and that the catalytic domain of the Rieske protein is swapped between the monomers, that is, the transmembrane helix interacts with one monomer and the catalytic domain with the other monomer. The connection between the membrane anchor and the catalytic domain is formed by a 12-residue flexible linker that allows for movement of the catalytic domain during the turnover of the enzyme (Fig. 8a see Section VII). Three different positional states of the catalytic domain of the Rieske protein have been observed in different crystal forms (Fig. 8b) (41, 42) ... 

The key CBB cycle enzyme, RubisCO, is the most abundant protein in the world [8], as it can comprise up to 50% of the total soluble protein in the chloro-plasts or in bacteria using this cycle. This fact is a consequence of the notorious catalytic inefficiency of RubisCO, that is, a low affinity for C02, a slow catalytic turnover rate, and a wasteful oxygenase side reaction responsible for photorespiration, resulting in a futile cleavage of the substrate to form phosphoglycolate as a side product. However, the CBB cycle enzymes are oxygen-insensitive and can easily be controlled, because the whole pathway is separated from... 

The cell walls of Gram-positive bacteria, including the pathogens S. aureus. Bacillus anthracis. Streptococcus pneumoniae, and Enterococcus faecalis contain thick layers of peptidoglycan. The peptidoglycan layers serve as both a protective barrier and as a scaffold for the attachment of secondary cell wall polymers and surface proteins. Surface proteins include hydrolytic enzymes involved in peptidoglycan turnover, as well as structures such as pili... 

An important aspect of mRNA regulation is determined by the turnover of mRNA molecules, i.e., translation can occur only as long as the mRNA remains intact. In bacteria, mRNA molecules have a lifetime of only a few minutes, and continued synthesis of mRNA molecules is needed to maintain synthesis of the proteins encoded in the mRNAs. In eukaryotes, the lifetime of mRNA is generally quite long (hours or days), thereby enabling a small number of transcription initiation events to produce proteins over a long period of time. 

L-protein The fiavin adenine dinucieotide-requiring protein of the giycine cieavage system, which functions to reoxidize dihydroiipoamide after each turnover, in various bacteria it is identicai with the E3 protein. Lipoyltransferase A protein that cataiyzes the transfer of the iipoyi group from iipoyi-AMP - or other activated forms of the moieouie - to LCPs. 

Classically, plants and bacteria have been the major sources for the purification of PLDs. The function of PLD in plants is not known although it may be involved in cell turnover and energy utilization during different cycles in plant life. Bacterial PLDs in some cases are toxins that can lead to severe cellular damage either alone or in combination with other proteins secreted from bacteria. These bacterial enzymes may also serve to help provide nutrients for the cell such as inorganic phosphate, as do the bacterial PLCs [2]. 

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