Clustering tendency in the protein fold space

Several non-redundant ensembles of protein three-dimensional structures were analyzed in order to estimate their natural clustering tendency by means of the Cox-Lewis coefficient. It was observed that, despite proteins tend to aggregate into different and well separated groups, some overlap between different clusters occurs. This suggests that classifications bases only on structural data cannot allow a systematic classification of proteins. Additional information are in particular needed in order to monitor completely the complex evolutionary relationships between proteins

Isoelectric points of multi-domain proteins

Although the distribution of protein isoelectric points is multi-modal, large proteins show isoelectric points less variable than small proteins and their isoelectric points tend to converge to a unique value, close to the pH of the milieu in which the proteins are functional, as far as the protein dimension increases. This study demonstrates that large proteins, which contain more than a single domain, do have isoelectric points less variable than small proteins, which contains a single domain. However, the distribution of the isoelectric points of the single domains, contained in large proteins, resembles that of small proteins, which contain a single domain. Thus, large proteins can be soluble even if their pI is very close to the pH of the milieu, in which they perform their function, since they can contain several domains, the electrostatic properties of each of which mirror those of small proteins

Lithium-Protein Interactions: Analysis of Lithium-Containing Protein Crystal Structures Deposited in the Protein Data Bank

Background: Despite the fact that lithium is not a biologically essential metallic element, its pharmacological properties are well known and human exposure to lithium is increasingly possible because of its used in aerospace industry and in batteries. Objective: Lithium-protein interactions are therefore interesting and the surveys of the structures of lithium-protein complexes is described in this paper. Methods: A high quality non-redundant set of lithium containing protein crystal structures was extracted from the Protein Data Bank and the stereochemistry of the lithium first coordination sphere was examined in detail. Results: Four main observations were reported: (i) lithium interacts preferably with oxygen atoms; (ii) preferably with side-chain atoms; (iii) preferably with Asp or Glu carboxylates; (iv) the coordination number tends to be four with stereochemical parameters similar to those observed in small molecules containing lithium. Conclusion: Although structural information on lithium-protein, available from the Protein Data Bank, is relatively scarce, these trends appears to be so clear that one may suppose that they will be confirmed by further data that will join the Protein Data Bank in the future

Consensus Prediction of Protein Conformational Disorder from Amino Acidic Sequence

Predictions of protein conformational disorder are important in structural biology since they can allow the elimination of protein constructs, the three-dimensional structure of which cannot be determined since they are natively unfolded. Here a new procedure is presented that allows one to predict with high accuracy disordered residues on the basis of protein sequences. It makes use of twelve prediction methods and merges their results by using least-squares optimization. A statistical survey of the Protein Data Bank is also reported, in order to know how many residues can be disordered in proteins that were crystallized and the three-dimensional structure of which was determined

Progress in the PRIDE technique for rapidly comparing protein three-dimensional structures

<p>Abstract</p> <p>Background</p> <p>Accurate and fast tools for comparing protein three-dimensional structures are necessary to scan and analyze large data sets.</p> <p>Findings</p> <p>The method described here is not only very fast but it is also reasonable precise, as it is shown by using the CATH database as a test set. Its rapidity depends on the fact that the protein structure is represented by vectors that monitors the distribution of the inter-residue distances within the protein core and the structure of which is optimized with the Freedman-Diaconis rule.</p> <p>Conclusion</p> <p>The similarity score is based on a <it>χ</it>²test, the probability density function of which can be accurately estimated.</p

Automated identification of chalcogen bonds in AlphaFold protein structure database files: is it possible?

Protein structure prediction and structural biology have entered a new era with an artificial intelligence-based approach encoded in the AlphaFold2 and the analogous RoseTTAfold methods. More than 200 million structures have been predicted by AlphaFold2 from their primary sequences and the models as well as the approach itself have naturally been examined from different points of view by experimentalists and bioinformaticians. Here, we assessed the degree to which these computational models can provide information on subtle structural details with potential implications for diverse applications in protein engineering and chemical biology and focused the attention on chalcogen bonds formed by disulphide bridges. We found that only 43% of the chalcogen bonds observed in the experimental structures are present in the computational models, suggesting that the accuracy of the computational models is, in the majority of the cases, insufficient to allow the detection of chalcogen bonds, according to the usual stereochemical criteria. High-resolution experimentally derived structures are therefore still necessary when the structure must be investigated in depth based on fine structural aspects

Hydration sites of unpaired RNA bases: a statistical analysis of the PDB structures

<p>Abstract</p> <p>Background</p> <p>Hydration is crucial for RNA structure and function. X-ray crystallography is the most commonly used method to determine RNA structures and hydration and, therefore, statistical surveys are based on crystallographic results, the number of which is quickly increasing.</p> <p>Results</p> <p>A statistical analysis of the water molecule distribution in high-resolution X-ray structures of unpaired RNA nucleotides showed that: different bases have the same penchant to be surrounded by water molecules; clusters of water molecules indicate possible hydration sites, which, in some cases, match those of the major and minor grooves of RNA and DNA double helices; complex hydrogen bond networks characterize the solvation of the nucleotides, resulting in a significant rigidity of the base and its surrounding water molecules. Interestingly, the hydration sites around unpaired RNA bases do not match, in general, the positions that are occupied by the second nucleotide when the base-pair is formed.</p> <p>Conclusions</p> <p>The hydration sites around unpaired RNA bases were found. They do not replicate the atom positions of complementary bases in the Watson-Crick pairs.</p