Global S&T Development Trend Analysis Platform of Resources and Environment
Analyses reveal a previously undescribed transmembrane protein fold in the endoplasmic reticulum-based glucosyltransferase ALG6 and provide a structural basis for understanding the glucose transfer mechanism.
In eukaryotic protein N-glycosylation, a series of glycosyltransferases catalyse the biosynthesis of a dolichylpyrophosphate-linked oligosaccharide before its transfer onto acceptor proteins(1). The final seven steps occur in the lumen of the endoplasmic reticulum (ER) and require dolichylphosphate-activated mannose and glucose as donor substrates(2). The responsible enzymes-ALG3, ALG9, ALG12, ALG6, ALG8 and ALG10-are glycosyltransferases of the C-superfamily (GT-Cs), which are loosely defined as containing membrane-spanning helices and processing an isoprenoid-linked carbohydrate donor substrate(3,4). Here we present the cryo-electron microscopy structure of yeast ALG6 at 3.0 angstrom resolution, which reveals a previously undescribed transmembrane protein fold. Comparison with reported GT-C structures suggests that GT-C enzymes contain a modular architecture with a conserved module and a variable module, each with distinct functional roles. We used synthetic analogues of dolichylphosphate-linked and dolichylpyrophosphate-linked sugars and enzymatic glycan extension to generate donor and acceptor substrates using purified enzymes of the ALG pathway to recapitulate the activity of ALG6 in vitro. A second cryo-electron microscopy structure of ALG6 bound to an analogue of dolichylphosphate-glucose at 3.9 angstrom resolution revealed the active site of the enzyme. Functional analysis of ALG6 variants identified a catalytic aspartate residue that probably acts as a general base. This residue is conserved in the GT-C superfamily. Our results define the architecture of ER-luminal GT-C enzymes and provide a structural basis for understanding their catalytic mechanisms.
Adipose tissue is an energy store and a dynamic endocrine organ(1,2). In particular, visceral adipose tissue (VAT) is critical for the regulation of systemic metabolism(3,4). Impaired VAT function-for example, in obesity-is associated with insulin resistance and type 2 diabetes(5,6). Regulatory T (T-reg) cells that express the transcription factor FOXP3 are critical for limiting immune responses and suppressing tissue inflammation, including in the VAT(7-9). Here we uncover pronounced sexual dimorphism in T-reg cells in the VAT. Male VAT was enriched for T-reg cells compared with female VAT, and T-reg cells from male VAT were markedly different from their female counterparts in phenotype, transcriptional landscape and chromatin accessibility. Heightened inflammation in the male VAT facilitated the recruitment of T-reg cells via the CCL2-CCR2 axis. Androgen regulated the differentiation of a unique IL-33-producing stromal cell population specific to the male VAT, which paralleled the local expansion of T-reg cells. Sex hormones also regulated VAT inflammation, which shaped the transcriptional landscape of VAT-resident T-reg cells in a BLIMP1 transcription factor-dependent manner. Overall, we find that sex-specific differences in T-reg cells from VAT are determined by the tissue niche in a sex-hormone-dependent manner to limit adipose tissue inflammation.
Visceral adipose tissue contains populations of regulatory T cells that exhibit sexual dimorphism, determined by the surrounding niche, and differ between male and female mice in terms of cell number, phenotype, transcriptional landscape and chromatin accessibility.
