Dataset Information

Identification of receptors for UNCG and GNRA Z-turns and their occurrence in rRNA.

ABSTRACT: In contrast to GNRA tetraloop receptors that are common in RNA, receptors for the more thermostable UNCG loops have remained elusive for almost three decades. An analysis of all RNA structures with resolution ?3.0 Å from the PDB allowed us to identify three previously unnoticed receptors for UNCG and GNRA tetraloops that adopt a common UNCG fold, named 'Z-turn' in agreement with our previously published nomenclature. These receptors recognize the solvent accessible second Z-turn nucleotide in different but specific ways. Two receptors participating in a complex network of tertiary interactions are associated with the rRNA UUCG and GAAA Z-turns capping helices H62 and H35a in rRNA large subunits. Structural comparison of fully assembled ribosomes and comparative sequence analysis of >6500 rRNA sequences helped us recognize that these motifs are almost universally conserved in rRNA, where they may contribute to organize the large subunit around the subdomain-IV four-way junction. The third UCCG receptor was identified in a rRNA/protein construct crystallized at acidic pH. These three non-redundant Z-turn receptors are relevant for our understanding of the assembly of rRNA and other long-non-coding RNAs, as well as for the design of novel folding motifs for synthetic biology.

SUBMITTER: D'Ascenzo L

PROVIDER: S-EPMC6125677 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Identification of receptors for UNCG and GNRA Z-turns and their occurrence in rRNA.

D'Ascenzo Luigi L Vicens Quentin Q Auffinger Pascal P

Nucleic acids research 20180901 15

In contrast to GNRA tetraloop receptors that are common in RNA, receptors for the more thermostable UNCG loops have remained elusive for almost three decades. An analysis of all RNA structures with resolution ≤3.0 Å from the PDB allowed us to identify three previously unnoticed receptors for UNCG and GNRA tetraloops that adopt a common UNCG fold, named 'Z-turn' in agreement with our previously published nomenclature. These receptors recognize the solvent accessible second Z-turn nucleotide in di ...[more]

PMID: 29986118

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Project description:The i + 5-->i hydrogen bonded turn conformation (pi-turn) with the fifth residue adopting alpha L conformation is frequently found at the C-terminus of helices in proteins and hence is speculated to be a "helix termination signal." An analysis of the occurrence of i + 5-->i hydrogen bonded turn conformation at any general position in proteins (not specifically at the helix C-terminus), using coordinates of 228 protein crystal structures determined by X-ray crystallography to better than 2.5 A resolution is reported in this paper. Of 486 detected pi-turn conformations, 367 have the (i + 4)th residue in alpha L conformation, generally occurring at the C-terminus of alpha-helices, consistent with previous observations. However, a significant number (111) of pi-turn conformations occur with (i + 4)th residue in alpha R conformation also, generally occurring in alpha-helices as distortions either at the terminii or at the middle, a novel finding. These two sets of pi-turn conformations are referred to by the names pi alpha L and pi alpha R-turns, respectively, depending upon whether the (i + 4)th residue adopts alpha L or alpha R conformations. Four pi-turns, named pi alpha L'-turns, were noticed to be mirror images of pi alpha L-turns, and four more pi-turns, which have the (i + 4)th residue in beta conformation and denoted as pi beta-turns, occur as a part of hairpin bend connecting twisted beta-strands. Consecutive pi-turns occur, but only with pi alpha R-turns. The preference for amino acid residues is different in pi alpha L and pi alpha R-turns. However, both show a preference for Pro after the C-termini. Hydrophilic residues are preferred at positions i + 1, i + 2, and i + 3 of pi alpha L-turns, whereas positions i and i + 5 prefer hydrophobic residues. Residue i + 4 in pi alpha L-turns is mainly Gly and less often Asn. Although pi alpha R-turns generally occur as distortions in helices, their amino acid preference is different from that of helices. Poor helix formers, such as His, Tyr, and Asn, also were found to be preferred for pi alpha R-turns, whereas good helix former Ala is not preferred. pi-Turns in peptides provide a picture of the pi-turn at atomic resolution. Only nine peptide-based pi-turns are reported so far, and all of them belong to pi alpha L-turn type with an achiral residue in position i + 4. The results are of importance for structure prediction, modeling, and de novo design of proteins.

Project description:BACKGROUND: For a proper understanding of protein structure and folding it is important to know if a polypeptide segment adopts a conformation inherent in the sequence or it depends on the context of its flanking secondary structures. Turns of various lengths have been studied and characterized starting from three-residue gamma-turn to six-residue pi-turn. The Schellman motif occurring at the C-terminal end of alpha-helices is a classical example of hydrogen bonded pi-turn involving residues at (i) and (i+5) positions. Hydrogen bonded and non-hydrogen bonded beta- and alpha-turns have been identified previously; likewise, a systematic characterization of pi-turns would provide valuable insight into turn structures. RESULTS: An analysis of protein structures indicates that at least 20% of pi-turns occur independent of the Schellman motif. The two categories of pi-turns, designated as pi-HB and SCH, have been further classified on the basis of backbone conformation and both have AAAa as the major class. They differ in the residue usage at position (i+1), the former having a large preference for Pro that is absent in the latter. As in the case of shorter length beta- and alpha-turns, pi-turns have also been identified not only on the basis of the existence of hydrogen bond, but also using the distance between terminal C alpha-atoms, and this resulted in a comparable number of non-hydrogen-bonded pi-turns (pi-NHB). The presence of shorter beta- and alpha-turns within all categories of pi-turns, the subtle variations in backbone torsion angles along the turn residues, the location of the turns in the context of tertiary structures have been studied. CONCLUSION: pi-turns have been characterized, first using hydrogen bond and the distance between C alpha atoms of the terminal residues, and then using backbone torsion angles. While the Schellman motif has a structural role in helix termination, many of the pi-HB turns, being located on surface cavities, have functional role and there is also sequence conservation.

Dataset Information

Identification of receptors for UNCG and GNRA Z-turns and their occurrence in rRNA.

Publications

Identification of receptors for UNCG and GNRA Z-turns and their occurrence in rRNA.

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