No abstract

A novel domain, GATE (Glycine-loop And Transducer Element), is identified in the ABC protein DrrA. This domain shows sequence and structural conservation among close homologs of DrrA as well as distantly-related ABC proteins. Among the highly conserved residues in this domain are three glycines, G215, G221 and G231, of which G215 was found to be critical for stable expression of the DrrAB complex. Other conserved residues, including E201, G221, K227 and G231, were found to be critical for the catalytic and transport functions of the DrrAB transporter. Structural analysis of both the previously published crystal structure of the DrrA homolog MalK and the modeled structure of DrrA showed that G215 makes close contacts with residues in and around the Walker A motif, suggesting that these interactions may be critical for maintaining the integrity of the ATP binding pocket as well as the complex. It is also shown that G215A or K227R mutation diminishes some of the atomic interactions essential for ATP catalysis and overall transport function. Therefore, based on both the biochemical and structural analyses, it is proposed that the GATE domain, located outside of the previously identified ATP binding and hydrolysis motifs, is an additional element involved in ATP catalysis.

Bacterial multidrug transporter DrrAB exhibits overlapping substrate specificity with mammalian Pglycoprotein. DrrA hydrolyzes ATP, and the energy is transduced to carrier DrrB resulting in export of drugs. Previous studies suggested that DrrB contains a large and flexible drug-binding pocket made of aromatic residues contributed by several transmembrane helices with different drugs binding to both specific and shared residues in this pocket. However, direct binding of drugs to DrrAB or the mechanism of substrate-induced conformational changes between DrrA and DrrB has so far not been investigated. We used two fluorescence-based approaches to determine substrate binding to purified DrrAB. Our analysis shows that DrrB binds drugs with variable affinities and contains multiple drug binding sites. This work also provides evidence for two asymmetric nucleotide binding sites in DrrA with strikingly different binding affinities. Using targeted fluorescence labeling, we provide clear evidence of long-range conformational changes occurring between DrrA and DrrB. It is proposed that the transduction pathway from the nucleotide-binding DrrA subunit to the substrate binding DrrB subunit includes Q-loop and CREEM motifs in DrrA and EAA-like motif in DrrB. This study lays a solid groundwork for examining roles of various conserved regions of DrrA and DrrB in transduction of conformational changes.

Molecular Microbial Metagenomics is a research-based undergraduate course developed at Georgia State University. This semester-long course provides hands-on research experience in the area of microbial diversity and introduces molecular approaches to study diversity. Students are part of an ongoing research project that uses metagenomic approaches to isolate clones containing 16S ribosomal ribonucleic acid (rRNA) genes from a soil metagenomic library. These approaches not only provide a measure of microbial diversity in the sample but may also allow discovery of novel organisms. Metagenomic approaches differ from the traditional culturing methods in that they use molecular analysis of community deoxyribonucleic acid (DNA) instead of culturing individual organisms. Groups of students select a batch of 100 clones from a metagenomic library. Using universal primers to amplify 16S rRNA genes from the pool of DNA isolated from 100 clones, and a stepwise process of elimination, each group isolates individual clones containing 16S rRNA genes within their batch of 100 clones. The amplified 16S rRNA genes are sequenced and analyzed using bioinformatics tools to determine whether the rRNA gene belongs to a novel organism. This course provides avenues for active learning and enhances students’ conceptual understanding of microbial diversity. Average scores on six assessment methods used during field testing indicated that success in achieving different learning objectives varied between 84% and 95%, with 65% of the students demonstrating complete grasp of the project based on the end-of-project lab report. The authentic research experience obtained in this course is also expected to result in more undergraduates choosing research-based graduate programs or careers.

Female sex hormones are known to regulate the immune functions of the female genital tract (FGT). While the majority of immune cells found in the FGT are T cells and Natural Killer cells (NK cells), very few studies have focused on NK cells in the FGT in contrast to numerous studies focusing on T-cells. Here, we characterized the distribution, phenotype and function of NK cells in FGT of HIV seronegative women using different mucosal sampling methods; cervicovaginal lavage (CVL), endocervical cytobrush (CB), and cervicovaginal biopsy and compared them to blood. We isolated cells from blood and FGT and performed multi-color flow cytometry to identify cellular phenotypes. First, we looked at the distribution of CD56brightand CD56dimpopulations of NK cells across the samples and found that CD56brightNK cells were lower in the FGT tissues compared to blood. Between the CD56brightand CD56dimpopulations, the CD56dimpopulation was significantly reduced in the follicular phase compared to the luteal phase in tissues. The NK cells within the FGT samples express higher levels of tissue resident markers CD69 and CD103. The co-expression of CD69+CD103+ markers seem to be significantly higher in follicular phase compared to luteal phase in tissues. These cells have high proliferative capacity with high levels of HLADR expression, suggesting that these cells are highly functional and activated. The gut tissue homing marker alpha4beta7 expression significantly reduced in the follicular phase, however other homing markers CCR5 and CCR7 expression were elevated in the follicular phase. Altogether, these data demonstrate that FGT is enriched with tissue resident NK cells with high activation and proliferation profile with distinct homing potential.