A molecular modeling study suggests that the controversial polycarbonate plastic building block bisphenol A may be less problematic as an endocrine-disrupting compound than one of its metabolites (PLoS One, DOI: 10.1371/journal.pone.0046078). BPA structurally resembles estradiol and binds weakly to estrogen receptors. Thus, BPA is thought to disrupt estrogen signaling and has been associated with health problems, including cancer, diabetes, and childhood obesity. In a 3-D modeling study, Michael E. Baker and Charlie Chandsawangbhuwana of the University of California, San Diego, found that a BPA metabolite known as MBP, which has three more carbon atoms between the phenol rings than does BPA, fits better into estrogen receptors than BPA itself. Previous studies have found that MBP binds 1,000 times more strongly than BPA. But the structural basis for the higher affinity hasn’t been determined. The UCSD researchers discovered that MBP’s longer structure allows both ends of the molecule to interact with amino acids in the receptors, just like estradiol does. Because it is shorter, BPA contacts the receptors only at one end. MBP levels in people should be monitored for possible health concerns, Baker says. He also suggests MBP could be used as a template to develop drugs that bind estrogen receptors to treat conditions linked to abnormal estrogen activity, such as breast and prostate cancers.