Extracellular synthesis of functional cyclodextrins (CDs) as intermediates of starch assimilation is a convenient microbial adaptation to sequester substrates, increase the half-life of the carbon source, carry bioactive compounds, and alleviate chemical toxicity through the formation of CD-guest complexes. Bacteria encoding the four steps of the carbohydrate metabolism pathway via cyclodextrins (CM-CD) actively internalize CDs across the microbial membrane via a putative type I ATP-dependent ABC sugar importer system, MdxEFG-(X/MsmX). While the first step of the CM-CD pathway encompasses extracellular starch-active cyclomaltodextrin glucanotransferases (CGTases) to synthesize linear dextrins and CDs, it is the ABC importer system in the second step that is the critical factor in determining which molecules from the CGTase activity will be internalized by the cell. Here, structure-function relationship studies of the cyclo⁄maltodextrin-binding protein MdxE of the MdxEFG-MsmX importer system from Thermoanaerobacter mathranii subsp. mathranii A3 are presented. Calorimetric and fluorescence studies of recombinant MdxE using linear dextrins and CDs showed that although MdxE binds linear dextrins and CDs with high affinity, the open-to-closed conformational change is solely observed after α- and β-CD binding, suggesting that the CM-CD pathway from Thermoanaerobacterales is exclusive for cellular internalization of these molecules. Structural analysis of MdxE coupled with docking simulations showed an overall architecture typically found in sugar-binding proteins (SBPs) that comprised two N- and C-domains linked by three small hinge regions, including the conserved aromatic triad Tyr193/Trp269/Trp378 in the C-domain and Phe87 in the N-domain involved in CD recognition and stabilization. Structural bioinformatic analysis of the entire MdxFG-MsmX importer system provided further insights into the binding, internalization, and delivery mechanisms of CDs. Hence, while the MdxE-CD complex couples to the permease subunits MdxFG to deliver the CD into the transmembrane channel, the dimerization of the cytoplasmatic promiscuous ATPase MsmX triggers active transport into the cytoplasm. This research provides the first results on a novel thermofunctional SBP and its role in the internalization of CDs in extremely thermophilic bacteria.

This study aimed to analyze the phytochemical composition of hexane extracts from Bixa orellana L. leaves using multivariate analysis and to evaluate their antimicrobial and antioxidant activities. A total of 74 compounds were identified by Gas chromatography–mass spectrometry (GC-MS) from three cultivars, Peruvian red (PR), Peruvian green (PG), and Criolla (Cr), collected in distinct regions of Campeche, Mexico: Bécal (Be), Calkiní (Ca), and Bacabchén (Ba). The chemical classes identified included sesquiterpenes, sesquiterpenoids, alkanes, quinones, tocopherols, and sterols. Principal component analysis (PCA) indicated a clear separation of PRCa, PRBa, and CrBe from the other samples, with 86% of the total variation explained by 22 components. In PRCa (+)-ledol, (E)-β-farnesene, germacrene D, cis-β-santalene, and α-bisabolol were found abundantly. PRBa showed an abundance of β-elemene and moderate levels of caryophyllene oxide, guaiol, and γ-sitosterol. CrBe contained abundant (−)-spathulenol and phytol. The antimicrobial activity against Staphylococcus aureus showed that PRCa extracts exhibited the largest inhibition zones (23.5 ± 2.12 mm), statistically influenced by geographic origin (p = 0.0005). Conversely, PRBe and PRBa showed higher total polyphenol content and antioxidant activity, with the geographic origin × variety interaction significantly influencing these traits (p < 0.001). The findings highlight the importance of B. orellana, particularly the Peruvian red variety, as a valuable source of bioactive secondary metabolites and underscore the influence of cultivar phenotype and geographic origin on phytochemical variability and its antimicrobial and antioxidant properties.