资源环境科技发展态势分析平台

Intracellular replication of the deadly pathogen Mycobacterium tuberculosis relies on the production of small organic molecules called siderophores that scavenge iron from host proteins(1). M. tuberculosis produces two classes of siderophore, lipid-bound mycobactin and water-soluble carboxymycobactin(2,3). Functional studies have revealed that iron-loaded carboxymycobactin is imported into the cytoplasm by the ATP binding cassette (ABC) transporter IrtAB(4), which features an additional cytoplasmic siderophore interaction domain(5). However, the predicted ABC exporter fold of IrtAB is seemingly contradictory to its import function. Here we show that membrane-reconstituted IrtAB is sufficient to import mycobactins, which are then reduced by the siderophore interaction domain to facilitate iron release. Structure determination by X-ray crystallography and cryo-electron microscopy not only confirms that IrtAB has an ABC exporter fold, but also reveals structural peculiarities at the transmembrane region of IrtAB that result in a partially collapsed inward-facing substrate-binding cavity. The siderophore interaction domain is positioned in close proximity to the inner membrane leaflet, enabling the reduction of membrane-inserted mycobactin. Enzymatic ATPase activity and in vivo growth assays show that IrtAB has a preference for mycobactin over carboxymycobactin as its substrate. Our study provides insights into an unusual ABC exporter that evolved as highly specialized siderophore-import machinery in mycobacteria.

Feeding controls a neuroimmune circuit comprising VIP-producing neurons and type-3 innate lymphoid cells that helps to regulate the efficiency of nutrient uptake and IL-22-mediated immune protection in the intestine.

An in vivo approach to identify proteins whose enrichment near cardiac Ca(V)1.2 channels changes upon beta-adrenergic stimulation finds the G protein Rad, which is phosphorylated by protein kinase A, thereby relieving channel inhibition by Rad and causing an increased Ca2+ current.

Increased cardiac contractility during the fight-or-flight response is caused by beta-adrenergic augmentation of Ca(V)1.2 voltage-gated calcium channels(1-4). However, this augmentation persists in transgenic murine hearts expressing mutant Ca(V)1.2 alpha(1C) and beta subunits that can no longer be phosphorylated by protein kinase A-an essential downstream mediator of beta-adrenergic signalling-suggesting that non-channel factors are also required. Here we identify the mechanism by which beta-adrenergic agonists stimulate voltage-gated calcium channels. We express alpha(1C) or beta(2B) subunits conjugated to ascorbate peroxidase(5) in mouse hearts, and use multiplexed quantitative proteomics(6,7) to track hundreds of proteins in the proximity of Ca(V)1.2. We observe that the calcium-channel inhibitor Rad(8,9), a monomeric G protein, is enriched in the Ca(V)1.2 microenvironment but is depleted during beta-adrenergic stimulation. Phosphorylation by protein kinase A of specific serine residues on Rad decreases its affinity for beta subunits and relieves constitutive inhibition of Ca(V)1.2, observed as an increase in channel open probability. Expression of Rad or its homologue Rem in HEK293T cells also imparts stimulation of Ca(V)1.3 and Ca(V)2.2 by protein kinase A, revealing an evolutionarily conserved mechanism that confers adrenergic modulation upon voltage-gated calcium channels.