Post-translational protein maturation

After their synthesis (translation), most proteins go through a maturation process, called post-translational modification that affects their activity. One common post-translational modification of proteins is phosphorylation. Two functional classes of enzymes mediate this reversible process protein kinases add phosphate groups to hydroxyl groups of serine, threonine and tyrosine in their substrate, while protein phosphatases remove phosphate groups. The phosphate-linking... 

Studies have shown that plants can make biologically active recombinant proteins through both transgenic and transient expression approaches. Although the plant post-translational machinery is similar to that of mammalian cells, there are some notable differences, e.g. differences in glycosylation, particularly the absence of sia-lation, which may impact the activity of certain proteins. The absence of mammalian enzymes may prevent complex maturation processes that are critical for the biological activity of proteins such as insulin. Fortunately these shortcomings affect the activity of only a limited number of proteins. 

The Golgi apparatus (3) is a complex network, also enclosed, consisting of flattened membrane saccules ( cisterns ), which are stacked on top of each other in layers. Proteins mature here and are sorted and packed. A distinction is made between the ds, medial, and trans Golgi regions, as well as a trans Golgi network (tGN). The post-translational modification of proteins, which starts in the ER, continues in these sections. 

Protease is responsible for cleaving these precursor molecules to produce the final structural proteins of the mature virion core. By preventing post-translational cleavage of the Gag-Pol polyprotein, protease inhibitors (Pis) prevent the processing of viral proteins into functional conformations, resulting in the production of immature, noninfectious viral particles (Figure 49-4). Protease inhibitors are active against both HIV-1 and HIV-2 unlike the NRTTs, however, they do not need intracellular activation. 

Protein maturation results in a mature protein in the proteome (post-translational modifications are possible here). 

The coding region of the type-L isozyme is 2898 base pairs long. It corresponds to 966 amino acid residues with a molecular weight of 109,648, and consists of two regions the amino-terminal extended sequence of 50 residues and the mature protein sequence of 916 residues. The amino acid sequence of the mature protein deduced from the cDNA structure is perfectly matched to the sequence chemically determined as described above. The stop codon, TAA, appeared at position 2942 in the cDNA sequence just after the carboxyl-terminal amino acid of the mature enzyme, indicating that no post-translational processing occurred at the carboxyl terminus. 

This review focuses upon the post-translational modification and chemical changes that occur in elastin. Outlined are the steps currently recognized as important in the assembly of pro-fibrillar elastin subunits into mature fibers. Descriptions of some of the proposed mechanisms that appear important to the process are also presented. It will be emphasized that from the standpoint of protein deterioration, elastin is a very novel protein. Under normal circumstances, the final product of elastin metabolism, the elastin fiber does not undergo degradation that is easily measured. Unlike the metabolism of many other proteins, deterioration or degradation is most evident biochemically in the initial stages of synthesis rather than as a consequence of maturation. Since the presence of crosslinks is an essential component of mature elastin, a section of this review also addresses important features of crosslink formation. 

Figure 2. Synthesis of mature elastin fibers. Some evidence suggests the possibility for proforms to elastin that appear as the first products of translation. These products are cleaved to tropoelastin (27), which appears to combine with microfibrillar protein. Although post-translational events important to the synthesis of the microfibrillar protein have not been defined, it is clear that it is a major component on which is organized or assembled the profibrillar forms of elastin. Cross-linking is catalyzed by lysyl oxidase, a copper-requiring protein (30). Recent information on the elastin proteinase(s) involved in tropoelastolysis would suggest that proteolysis may also play a role in elastin fiber...

For a protein substance, the complete mature amino acid sequence in a format that can be copied for analysis (Word or in the text of an e-mail) and with spaces between groups of 10 characters, and the sequence length the general information on disulfides and all post-translational modification. 

MnSODs and FeSODs from most procaryotic organisms are dimeric while MnSODs from mitochondria and some thermophilic bacteria are tetrameric [21]. However, mitochondrial MnSOD from Caenorhahditis elegans was found to be dimeric [22]. Eukaryotic MnSOD is a tetrameric protein encoded in the nucleus, synthesized in the cystosol, and imported post-translationally into the mitochondrial matrix. The 25 kDa precursor protein has a mitochondrial transit peptide that is cleaved to produce the mature 22 kDa subunit. The mature protein exists as a tetramer, each subunit containing one Mn ion. The mitochondrial MnSOD primary sequences are highly homologous to the prokaryotic Mn- and FeSOD, but has no resemblance to the CuZnSODs [23]. In MnSODs and FeSODs, the metal ions are coordinated by three His N atoms and one Asp O atom [24]. 

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