The Pfam protein families database: towards a more sustainable future

In the last two years the Pfam database (http://pfam.xfam.org) has undergone a substantial reorganisation to reduce the effort involved in making a release, thereby permitting more frequent releases. Arguably the most significant of these changes is that Pfam is now primarily based on the UniProtKB reference proteomes, with the counts of matched sequences and species reported on the website restricted to this smaller set. Building families on reference proteomes sequences brings greater stability, which decreases the amount of manual curation required to maintain them. It also reduces the number of sequences displayed on the website, whilst still providing access to many important model organisms. Matches to the full UniProtKB database are, however, still available and Pfam annotations for individual UniProtKB sequences can still be retrieved. Some Pfam entries (1.6%) which have no matches to reference proteomes remain; we are working with UniProt to see if sequences from them can be incorporated into reference proteomes. Pfam-B, the automatically-generated supplement to Pfam, has been removed. The current release (Pfam 29.0) includes 16 295 entries and 559 clans. The facility to view the relationship between families within a clan has been improved by the introduction of a new tool.

Structure and computational analysis of a novel protein with metallopeptidase-like and circularly permuted winged-helix-turn-helix domains reveals a possible role in modified polysaccharide biosynthesis

Background

CA_C2195 from Clostridium acetobutylicum is a protein of unknown function. Sequence analysis predicted that part of the protein contained a metallopeptidase-related domain. There are over 200 homologs of similar size in large sequence databases such as UniProt, with pairwise sequence identities in the range of ~40-60%. CA_C2195 was chosen for crystal structure determination for structure-based function annotation of novel protein sequence space.

Results

The structure confirmed that CA_C2195 contained an N-terminal metallopeptidase-like domain. The structure revealed two extra domains: an α+β domain inserted in the metallopeptidase-like domain and a C-terminal circularly permuted winged-helix-turn-helix domain.

Conclusions

Based on our sequence and structural analyses using the crystal structure of CA_C2195 we provide a view into the possible functions of the protein. From contextual information from gene-neighborhood analysis, we propose that rather than being a peptidase, CA_C2195 and its homologs might play a role in biosynthesis of a modified cell-surface carbohydrate in conjunction with several sugar-modification enzymes. These results provide the groundwork for the experimental verification of the function.

New mini- zincin structures provide a minimal scaffold for members of this metallopeptidase superfamily

BACKGROUND

The Acel_2062 protein from Acidothermus cellulolyticus is a protein of unknown function. Initial sequence analysis predicted that it was a metallopeptidase from the presence of a motif conserved amongst the Asp-zincins, which are peptidases that contain a single, catalytic zinc ion ligated by the histidines and aspartic acid within the motif (HEXXHXXGXXD). The Acel_2062 protein was chosen by the Joint Center for Structural Genomics for crystal structure determination to explore novel protein sequence space and structure-based function annotation.

RESULTS

The crystal structure confirmed that the Acel_2062 protein consisted of a single, zincin-like metallopeptidase-like domain. The Met-turn, a structural feature thought to be important for a Met-zincin because it stabilizes the active site, is absent, and its stabilizing role may have been conferred to the C-terminal Tyr113. In our crystallographic model there are two molecules in the asymmetric unit and from size-exclusion chromatography, the protein dimerizes in solution. A water molecule is present in the putative zinc-binding site in one monomer, which is replaced by one of two observed conformations of His95 in the other.

CONCLUSIONS

The Acel_2062 protein is structurally related to the zincins. It contains the minimum structural features of a member of this protein superfamily, and can be described as a "mini- zincin". There is a striking parallel with the structure of a mini-Glu-zincin, which represents the minimum structure of a Glu-zincin (a metallopeptidase in which the third zinc ligand is a glutamic acid). Rather than being an ancestral state, phylogenetic analysis suggests that the mini-zincins are derived from larger proteins.

Pfam: the protein families database

Pfam, available via servers in the UK (http://pfam.sanger.ac.uk/) and the USA (http://pfam.janelia.org/), is a widely used database of protein families, containing 14 831 manually curated entries in the current release, version 27.0. Since the last update article 2 years ago, we have generated 1182 new families and maintained sequence coverage of the UniProt Knowledgebase (UniProtKB) at nearly 80%, despite a 50% increase in the size of the underlying sequence database. Since our 2012 article describing Pfam, we have also undertaken a comprehensive review of the features that are provided by Pfam over and above the basic family data. For each feature, we determined the relevance, computational burden, usage statistics and the functionality of the feature in a website context. As a consequence of this review, we have removed some features, enhanced others and developed new ones to meet the changing demands of computational biology. Here, we describe the changes to Pfam content. Notably, we now provide family alignments based on four different representative proteome sequence data sets and a new interactive DNA search interface. We also discuss the mapping between Pfam and known 3D structures.

Two Pfam protein families characterized by a crystal structure of protein lpg2210 from Legionella pneumophila

Background

Every genome contains a large number of uncharacterized proteins that may encode entirely novel biological systems. Many of these uncharacterized proteins fall into related sequence families. By applying sequence and structural analysis we hope to provide insight into novel biology.

Results

We analyze a previously uncharacterized Pfam protein family called DUF4424 [Pfam:PF14415]. The recently solved three-dimensional structure of the protein lpg2210 from Legionella pneumophila provides the first structural information pertaining to this family. This protein additionally includes the first representative structure of another Pfam family called the YARHG domain [Pfam:PF13308]. The Pfam family DUF4424 adopts a 19-stranded beta-sandwich fold that shows similarity to the N-terminal domain of leukotriene A-4 hydrolase. The YARHG domain forms an all-helical domain at the C-terminus. Structure analysis allows us to recognize distant similarities between the DUF4424 domain and individual domains of M1 aminopeptidases and tricorn proteases, which form massive proteasome-like capsids in both archaea and bacteria.

Conclusions

Based on our analyses we hypothesize that the DUF4424 domain may have a role in forming large, multi-component enzyme complexes. We suggest that the YARGH domain may play a role in binding a moiety in proximity with peptidoglycan, such as a hydrophobic outer membrane lipid or lipopolysaccharide.

The LRC haplotype project: a resource for killer immunoglobulin-like receptor-linked association studies

There is increasing evidence for epistatic interactions between gene products (e.g. KIR) encoded within the Leukocyte Receptor Complex (LRC) with those (e.g. HLA) of the Major Histocompatibility Complex (MHC), resulting in susceptibility to disease. Identification of such associations at the DNA level requires comprehensive knowledge of the genetic variation and haplotype structure of the underlying loci. The LRC haplotype project aims to provide this knowledge by sequencing common LRC haplotypes.

The genomic sequence and analysis of the swine major histocompatibility complex

We describe the generation and analysis of an integrated sequence map of a 2.4-Mb region of pig chromosome 7, comprising the classical class I region, the extended and classical class II regions, and the class III region of the major histocompatibility complex (MHC), also known as swine leukocyte antigen (SLA) complex. We have identified and manually annotated 151 loci, of which 121 are known genes (predicted to be functional), 18 are pseudogenes, 8 are novel CDS loci, 3 are novel transcripts, and 1 is a putative gene. Nearly all of these loci have homologues in other mammalian genomes but orthologues could be identified with confidence for only 123 genes. The 28 genes (including all the SLA class I genes) for which unambiguous orthology to genes within the human reference MHC could not be established are of particular interest with respect to porcine-specific MHC function and evolution. We have compared the porcine MHC to other mammalian MHC regions and identified the differences between them. In comparison to the human MHC, the main differences include the absence of HLA-A and other class I-like loci, the absence of HLA-DP-like loci, and the separation of the extended and classical class II regions from the rest of the MHC by insertion of the centromere. We show that the centromere insertion has occurred within a cluster of BTNL genes located at the boundary of the class II and III regions, which might have resulted in the loss of an orthologue to human C6orf10 from this region.

Analysis of the genomic region containing the tammar wallaby (Macropus eugenii) orthologues of MHC class III genes

Major histocompatibility complex (MHC) molecules are central to development and regulation of the immune system in all jawed vertebrates. MHC class III cytokine genes from the tumor necrosis factor core family, including tumor necrosis factor (TNF) and lymphotoxin alpha and beta (LTA, LTB), are well studied in human and mouse. Orthologues have been identified in several other eutherian species and the cDNA sequences have been reported for a model marsupial, the tammar wallaby. Comparative genomics can help to determine gene function, to understand the evolution of a gene or gene family, and to identify potential regulatory regions. We therefore cloned the genomic region containing the tammar LTB, TNF, and LTA orthologues by "genome walking", using primers designed from known tammar sequences and regions conserved in other species. We isolated two tammar BAC clones containing all three genes. These tammar genes show similar intergenic distances and the same transcriptional orientation as in human and mouse. Gene structures and sequences are also very conserved. By comparing the tammar, human and mouse genomic sequences we were able to identify candidate regulatory regions for these genes in mammals. Full length sequencing of BACs containing the three genes has been partially completed, and reveals the presence of a number of other tammar MHC III orthologues in this region.