Peer-led team-learning (PLTL) groups have been implemented in both semesters of the general chemistry series at Washington University. We have adapted the PLTL model to fit into a traditional university structure (classes are large; there are multiple sections with different instructors; and graduate students are teaching assistants in the course) by establishing an optional PLTL program outside the course structure. Using data from the fall semesters of 2003 and 2004, we found that students who participated in PLTL groups performed approximately one-third of a grade point (an average of B versus B-) higher in our first-semester General Chemistry course compared with students who opted not to participate, even after controlling for differences in the students' background characteristics. These results of PLTL's effect on students' performance and attitudes correspond to those found in PLTL programs elsewhere. This improved performance was obtained even though our PLTL-participating students were less prepared quantitatively than our non-PLTL-participating students. In addition, we conducted an attitudinal study, and found that students participating in the PLTL program reported having positive attitudes about the program and the effects of PLTL on their performance in the class. We also found some gender difference in attitudes towards group study and interactions.

De novo purine biosynthesis proceeds by two divergent paths. In bacteria, yeasts, and plants, 5-aminoimidazole ribonucleotide (AIR) is converted to 4-carboxy-AIR (CAIR) by two enzymes: N(5)-carboxy-AIR (N(5)-CAIR) synthetase (PurK) and N(5)-CAIR mutase (class I PurE). In animals, the conversion of AIR to CAIR requires a single enzyme, AIR carboxylase (class II PurE). The CAIR carboxylate derives from bicarbonate or CO(2), respectively. Class I PurE is a promising antimicrobial target. Class I and class II PurEs are mechanistically related but bind different substrates. The spirochete dental pathogen Treponema denticola lacks a purK gene and contains a class II purE gene, the hallmarks of CO(2)-dependent CAIR synthesis. We demonstrate that T. denticola PurE (TdPurE) is AIR carboxylase, the first example of a prokaryotic class II PurE. Steady-state and pre-steady-state experiments show that TdPurE binds AIR and CO(2) but not N(5)-CAIR. Crystal structures of TdPurE alone and in complex with AIR show a conformational change in the key active site His40 residue that is not observed for class I PurEs. A contact between the AIR phosphate and a differentially conserved residue (TdPurE Lys41) enforces different AIR conformations in each PurE class. As a consequence, the TdPurE·AIR complex contains a portal that appears to allow the CO(2) substrate to enter the active site. In the human pathogen T. denticola, purine biosynthesis should depend on available CO(2) levels. Because spirochetes lack carbonic anhydrase, the corresponding reduction in bicarbonate demand may confer a selective advantage.