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Urine-based biomarkers for non-invasive diagnosis of bladder cancer are urgently needed. No single marker with sufficient sensitivity and specificity has been described so far. Thus, a combination of markers appears to be a promising approach. The aim of this case-control study was to evaluate the performance of an in-house developed enzyme-linked immunosorbent assay (ELISA) for survivin, the UBC® Rapid test, and the combination of both assays. A total of 290 patients were recruited. Due to prior bladder cancer, 46 patients were excluded. Urine samples were available from 111 patients with bladder cancer and 133 clinical controls without urologic diseases. Antibodies generated from recombinant survivin were utilized to develop a sandwich ELISA. The ELISA and the UBC® Rapid test were applied to all urine samples. Receiver operating characteristic (ROC) analysis was used to evaluate marker performance. The survivin ELISA exhibited a sensitivity of 35% with a specificity of 98%. The UBC® Rapid test showed a sensitivity of 56% and a specificity of 96%. Combination of both assays increased the sensitivity to 66% with a specificity of 95%. For high-grade tumors, the combination showed a sensitivity of 82% and a specificity of 95%. The new survivin ELISA and the UBC® Rapid test are both able to detect bladder cancer, especially high-grade tumors. However, the performance of each individual marker is moderate and efforts to improve the survivin assay should be pursued. A combination of both assays confirmed the benefit of using marker panels. The results need further testing in a prospective study and with a high-risk population.

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SummaryThe membrane lipid phosphatidylcholine (PC) is crucial for stress adaptation and virulence of the plant pathogen Agrobacterium tumefaciens. The phospholipid N-methyltransferase PmtA catalyzes three successive methylations of phosphatidylethanolamine to yield PC. Here, we asked how PmtA is recruited to its site of action, the inner leaflet of the membrane. We found that the enzyme attaches to the membrane via electrostatic interactions with anionic lipids, which do not serve as substrate for PmtA. Increasing PC concentrations trigger membrane dissociation suggesting that membrane binding of PmtA is negatively regulated by its end product PC. Two predicted alphahelical regions (αA and αF) contribute to membrane binding of PmtA. The N-terminal helix αA binds anionic lipids in vitro with higher affinity than the central helix αF. The latter undergoes a structural transition from disordered to α-helical conformation in the presence of anionic lipids. The basic amino acids R8 and K12 and the hydrophobic amino acid F19 are critical for membrane binding by αA as well as for activity of full-length PmtA. We conclude that a combination of electrostatic and hydrophobic forces is responsible for membrane association of the phospholipid-modifying enzyme.

The presence of the membrane lipid phosphatidylcholine (PC) in the bacterial membrane is critically important for many host-microbe interactions. The phospholipid N-methyltransferase PmtA from the plant pathogen Agrobacterium tumefaciens catalyzes the formation of PC by a three-step methylation of phosphatidylethanolamine via monomethylphosphatidylethanolamine and dimethylphosphatidylethanolamine. The methyl group is provided by S-adenosylmethionine (SAM), which is converted to S-adenosylhomocysteine (SAH) during transmethylation. Despite the biological importance of bacterial phospholipid N-methyltransferases, little is known about amino acids critical for binding to SAM or phospholipids and catalysis. Alanine substitutions in the predicted SAM-binding residues E58, G60, G62, and E84 in A. tumefaciens PmtA dramatically reduced SAM-binding and enzyme activity. Homology modeling of PmtA satisfactorily explained the mutational results. The enzyme is predicted to exhibit a consensus topology of the SAM-binding fold consistent with cofactor interaction as seen with most structurally characterized SAM-methyltransferases. Nuclear magnetic resonance (NMR) titration experiments and 14 C-SAM-binding studies revealed binding constants for SAM and SAH in the low micromolar range. Our study provides first insights into structural features and SAM binding of a bacterial phospholipid N-methyltransferase.