N-Terminal Modifikation and Amino-Acid Sequence of the Ribosomal Protein HmaS7 from<i>Haloarcula marismortui</i>and Homology Studies to other Ribosomal Proteins

Klussmann, Sven; Franke, P.; Bergmann, Ulrike; Kostka, Susanne; Wittmann‐Liebold, Brigitte

doi:10.1515/bchm3.1993.374.1-6.305

Cited by 8 publications

(6 citation statements)

References 9 publications

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“…Furthermore, only a few proteins are known to be modified in this manner, including glutamate dehydrogenase-2 (GDH-2) (28) and Alba1 chromatin proteins of Sulfolobus solfataricus (4); ribosomal proteins S7P, L31e, and S19P of Haloarcula marismortui (18,22,26); and halocyanin of Natronobacterium pharaonis (31). The majority of these modifications are on N-terminal serine residues, exposed by a presumed methionine aminopeptidase and preceding either Ser or Ala (Ser-Ser/Ala) residues.…”

Section: Discussionmentioning

confidence: 99%

Posttranslational Modification of the 20S Proteasomal Proteins of the Archaeon Haloferax volcanii

2006

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20S proteasomes are large, multicatalytic proteases that play an important role in intracellular protein degradation. The barrel-like architecture of 20S proteasomes, formed by the stacking of four heptameric protein rings, is highly conserved from archaea to eukaryotes. The outer two rings are composed of ␣-type subunits, and the inner two rings are composed of ␤-type subunits. The halophilic archaeon Haloferax volcanii synthesizes two different ␣-type proteins, ␣1 and ␣2, and one ␤-type protein that assemble into at least two 20S proteasome subtypes. In this study, we demonstrate that all three of these 20S proteasomal proteins (␣1, ␣2, and ␤) are modified either post-or cotranslationally. Using electrospray ionization quadrupole time-of-flight mass spectrometry, a phosphorylation site of the ␤ subunit was identified at Ser129 of the deduced protein sequence. In addition, ␣1 and ␣2 contained N-terminal acetyl groups. These findings represent the first evidence of acetylation and phosphorylation of archaeal proteasomes and are one of the limited examples of post-and/or cotranslational modification of proteins in this unusual group of organisms.26S proteasomes are central proteolytic enzymes of the ubiquitin-mediated degradation pathway in eukaryotes. The 20S core particle of 26S proteasomes is responsible for the hydrolysis of peptide bonds, and the overall architecture of this complex is conserved from archaea to eukaryotes (12). The 20S proteasomes are chambered proteases with the proteolytic N-terminal Thr active site sequestered within a cylindrical complex composed of 28 proteins associated as four heptameric rings of ␣-and ␤-type subunits (2). The ␣-type subunits form the outer two rings, and the ␤-type subunits form the inner two rings that comprise the central proteolytic chamber.In the halophilic archaeon Haloferax volcanii, there are two ␣-type (␣1 and ␣2) subunits and one ␤-type proteasomal subunit (54). The N-terminal protein sequence of the ␤ subunit purified from 20S proteasomes reveals an N-terminal Thr residue exposed via posttranslational cleavage which is likely to form the active site (54). In contrast, the ␣ subunits are not amenable to N-terminal sequencing, suggesting that these proteins are modified at their N termini (54).Two subtypes of 20S proteasome complexes have been identified in stationary-phase cells and are denoted ␣1␤-and ␣1␤␣2-20S, with the latter containing both ␣-type subunits in a single 20S proteasome (20). Interestingly, both ␣1 and ␣2 proteins form homo-oligomeric rings and ␣1-␣1 and ␣2-␣2 contacts (versus ␣1-␣2 contacts) are detected in 20S proteasome complexes (20). Thus, the ␣1␤␣2-20S core particle is proposed to be an asymmetric proteasome, with the stacked rings arranged in an ␣1:␤:␤:␣2 configuration. The ␣1␤-20S proteasome, in contrast, is in a symmetrical ␣1:␤:␤:␣1 configuration. The levels of ␣2 protein increase severalfold, while the levels of ␣1 and ␤ proteins remain relatively constant as cells enter stationary phase (41). This is likely to allow for the regul...

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Section: Discussionmentioning

confidence: 99%

Posttranslational Modification of the 20S Proteasomal Proteins of the Archaeon Haloferax volcanii

2006

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“…Already 20 years ago it was reported that a few ribosomal proteins of haloarchaea are acetylated at their N-terminus [24–26]. However, this did not increase the interest in protein acetylation in archaea because on the one hand it perfectly fitted to the bacterial paradigm and thus seemed to underscore that protein acetylation is a rare event also in archaea, and on the other hand only extremely few reports about the acetylation of archaeal proteins appeared.…”

Section: N-terminal Protein Acetylation In the Archaeamentioning

confidence: 99%

Protein Acetylation in Archaea, Bacteria, and Eukaryotes

Soppa

2010

Archaea

110

106

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Proteins can be acetylated at the alpha-amino group of the N-terminal amino acid (methionine or the penultimate amino acid after methionine removal) or at the epsilon-amino group of internal lysines. In eukaryotes the majority of proteins are N-terminally acetylated, while this is extremely rare in bacteria. A variety of studies about N-terminal acetylation in archaea have been reported recently, and it was revealed that a considerable fraction of proteins is N-terminally acetylated in haloarchaea and Sulfolobus, while this does not seem to apply for methanogenic archaea. Many eukaryotic proteins are modified by differential internal acetylation, which is important for a variety of processes. Until very recently, only two bacterial proteins were known to be acetylation targets, but now 125 acetylation sites are known for E. coli. Knowledge about internal acetylation in archaea is extremely limited; only two target proteins are known, only one of which—Alba—was used to study differential acetylation. However, indications accumulate that the degree of internal acetylation of archaeal proteins might be underestimated, and differential acetylation has been shown to be essential for the viability of haloarchaea. Focused proteomic approaches are needed to get an overview of the extent of internal protein acetylation in archaea.

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“…2 Due to the lack of systematic studies, the latter was also anticipated to hold true for archaea, since N-terminal acetylation has only rarely been described in archaea so far. [7][8][9][10] Another type of N-terminal processing is the cleavage of a signal sequence, which is found for extracellular proteins as well as for proteins targeted to eukaryotic cell compartments and membranes. While integral membrane proteins of the outer membrane carry a signal sequence in bacteria, those of the inner membrane lack cleavable signal sequences.…”

Section: Introductionmentioning

confidence: 99%

Archaeal N-terminal Protein Maturation Commonly Involves N-terminal Acetylation: A Large-scale Proteomics Survey

Falb

Aivaliotis

Garcia-Rizo

et al. 2006

Journal of Molecular Biology

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N-Terminal Modifikation and Amino-Acid Sequence of the Ribosomal Protein HmaS7 fromHaloarcula marismortuiand Homology Studies to other Ribosomal Proteins

Cited by 8 publications

References 9 publications

Posttranslational Modification of the 20S Proteasomal Proteins of the Archaeon Haloferax volcanii

Posttranslational Modification of the 20S Proteasomal Proteins of the Archaeon Haloferax volcanii

Protein Acetylation in Archaea, Bacteria, and Eukaryotes

Archaeal N-terminal Protein Maturation Commonly Involves N-terminal Acetylation: A Large-scale Proteomics Survey

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