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Background: ␣-L-Rhamnosidase hydrolyzes ␣-linked L-rhamnose from rhamnoglycosides or polysaccharides. Results: The crystal structure of Streptomyces avermitilis ␣-L-rhamnosidase belonging to glycoside hydrolase family 78 was determined. Conclusion:The L-rhamnose complexed structure revealed the catalytic mechanism of the enzyme and a calcium-dependent carbohydrate-binding module. Significance: Efficient catalysis of an exo-rhamnosidase requires a novel carbohydrate-binding module that binds terminal L-rhamnose sugars.

Mannosidases catalyze the hydrolysis of a diverse range of polysaccharides and glycoconjugates, and the various sequence-based mannosidase families have evolved ingenious strategies to overcome the stereoelectronic challenges of mannoside chemistry. Using a combination of computational chemistry, inhibitor design and synthesis, and X-ray crystallography of inhibitor/enzyme complexes, it is demonstrated that mannoimidazole-type inhibitors are energetically poised to report faithfully on mannosidase transition-state conformation, and provide direct evidence for the conformational itinerary used by diverse mannosidases, including β-mannanases from families GH26 and GH113. Isofagomine-type inhibitors are poor mimics of transition-state conformation, owing to the high energy barriers that must be crossed to attain mechanistically relevant conformations, however, these sugar-shaped heterocycles allow the acquisition of ternary complexes that span the active site, thus providing valuable insight into active-site residues involved in substrate recognition.

Background A pattern of major and minor congenital anomalies, facial dysmorphic features, and neurodevelopmental difficulties, including cognitive and social impairments has been reported in some children exposed to sodium valproate (VPA) during pregnancy. Recognition of the increased risks of in utero exposure to VPA for congenital malformations, and for the neurodevelopmental effects in particular, has taken many years but these are now acknowledged following the publication of the outcomes of several prospective studies and registries. As with other teratogens, exposure to VPA can have variable effects, ranging from a characteristic pattern of major malformations and significant intellectual disability to the other end of the continuum, characterised by facial dysmorphism which is often difficult to discern and a more moderate effect on neurodevelopment and general health. It has become clear that some individuals with FVSD have complex needs requiring multidisciplinary care but information regarding management is currently lacking in the medical literature. Methods An expert group was convened by ERN-ITHACA, the European Reference Network for Congenital Malformations and Intellectual Disability comprised of professionals involved in the care of individuals with FVSD and with patient representation. Review of published and unpublished literature concerning management of FVSD was undertaken and the level of evidence from these sources graded. Management recommendations were made based on strength of evidence and consensus expert opinion, in the setting of an expert consensus meeting. These were then refined using an iterative process and wider consultation. Results Whilst there was strong evidence regarding the increase in risk for major congenital malformations and neurodevelopmental difficulties there was a lack of high level evidence in other areas and in particular in terms of optimal clinical management.. The expert consensus approach facilitated the formulation of management recommendations, based on literature evidence and best practice. The outcome of the review and group discussions leads us to propose the term Fetal Valproate Spectrum Disorder (FVSD) as we feel this better encompasses the broad range of effects seen following VPA exposure in utero. Conclusion The expert consensus approach can be used to define the best available clinical guidance for the diagnosis and management of rare disorders such as FVSD. FVSD can have medical, developmental and neuropsychological impacts with life-long consequences and affected individuals benefit from the input of a number of different health professionals. Electronic supplementary material The online version of this article (10.1186/s13023-019-1064-y) contains supplementary material, which is available to authorized users.

Genetic studies of intellectual disability and identification of monogenic causes of obesity in humans have made immense contribution toward the understanding of the brain and control of body mass. The leptin > melanocortin > SIM1 pathway is dysregulated in multiple monogenic human obesity syndromes but its downstream targets are still unknown. In ten individuals from six families, with overlapping 6q16.1 deletions, we describe a disorder of variable developmental delay, intellectual disability, and susceptibility to obesity and hyperphagia. The 6q16.1 deletions segregated with the phenotype in multiplex families and were shown to be de novo in four families, and there was dramatic phenotypic overlap among affected individuals who were independently ascertained without bias from clinical features. Analysis of the deletions revealed a ∼350 kb critical region on chromosome 6q16.1 that encompasses a gene for proneuronal transcription factor POU3F2, which is important for hypothalamic development and function. Using morpholino and mutant zebrafish models, we show that POU3F2 lies downstream of SIM1 and controls oxytocin expression in the hypothalamic neuroendocrine preoptic area. We show that this finding is consistent with the expression patterns of POU3F2 and related genes in the human brain. Our work helps to further delineate the neuro-endocrine control of energy balance/body mass and demonstrates that this molecular pathway is conserved across multiple species.