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As an ancient protein family, the WD40 repeat proteins often play essential roles in fundamental cellular processes in eukaryotes. Although investigations of eukaryotic WD40 proteins have been frequently reported, prokaryotic ones remain largely uncharacterized. In this paper, we report a systematic analysis of prokaryotic WD40 proteins and detailed comparisons with eukaryotic ones. About 4,000 prokaryotic WD40 proteins have been identified, accounting for 6.5% of all WD40s. While their abundances are less than 0.1% in most prokaryotes, they are enriched in certain species from Cyanobacteria and Planctomycetes, and participate in various functions such as prokaryotic signal transduction and nutrient synthesis. Comparisons show that a higher proportion of prokaryotic WD40s tend to contain multiple WD40 domains and a large number of hydrogen bond networks. The observation that prokaryotic WD40 proteins tend to show high internal sequence identity suggests that a substantial proportion of them (~20%) should be formed by recent or young repeat duplication events. Further studies demonstrate that the very young WD40 proteins, i.e., Highly-Repetitive WD40s, should be of higher stability. Our results have presented a catalogue of prokaryotic WD40 proteins, and have shed light on their evolutionary origins.

The WD40 proteins, often acting as scaffolds to form functional complexes in fundamental cellular processes, are one of the largest families encoded by the eukaryotic genomes. Systematic studies of this family on genome scale are highly required for understanding their detailed functions, but are currently lacking in the animal lineage. Here we present a comprehensive in silico study of the human WD40 family. We have identified 262 non-redundant WD40 proteins, and grouped them into 21 classes according to their domain architectures. Among them, 11 animal-specific domain architectures have been recognized. Sequence alignment indicates the complicated duplication and recombination events in the evolution of this family. Through further phylogenetic analysis, we have revealed that the WD40 family underwent more expansion than the overall average in the evolutionary early stage, and the early emerged WD40 proteins are prone to domain architectures with fundamental cellular roles and more interactions. While most widely and highly expressed human WD40 genes originated early, the tissue-specific ones often have late origin. These results provide a landscape of the human WD40 family concerning their classification, evolution, and expression, serving as a valuable complement to the previous studies in the plant lineage.

Determination of variant pathogenicity represents a major challenge in the era of high-throughput sequencing. Erroneous categorization may result if variants affect genes that are in fact dispensable. We demonstrate that this also applies to rare, apparently unambiguous truncating mutations of an established disease gene. By whole-exome sequencing (WES) in a consanguineous family with congenital non-syndromic deafness, we unexpectedly identified a homozygous nonsense variant, p.Arg1066*, in AHI1, a gene associated with Joubert syndrome (JBTS), a severe recessive ciliopathy. None of four homozygotes expressed any signs of JBTS, and one of them had normal hearing, which also ruled out p.Arg1066* as the cause of deafness. Homozygosity mapping and WES in the only other reported JBTS family with a homozygous C-terminal truncation (p.Trp1088Leufs*16) confirmed AHI1 as disease gene, but based on a more N-terminal missense mutation impairing WD40-repeat formation. Morpholinos against N-terminal zebrafish Ahi1, orthologous to where human mutations cluster, produced a ciliopathy, but targeting near human p.Arg1066 and p.Trp1088 did not. Most AHI1 mutations in JBTS patients result in truncated protein lacking WD40-repeats and the SH3 domain; disease was hitherto attributed to loss of these protein interaction modules. Our findings indicate that normal development does not require the C-terminal SH3 domain. This has far-reaching implications, considering that variants like p.Glu984* identified by preconception screening ('Kingsmore panel') do not necessarily indicate JBTS carriership. Genomes of individuals with consanguineous background are enriched for homozygous variants that may unmask dispensable regions of disease genes and unrecognized false positives in diagnostic large-scale sequencing and preconception carrier screening.