When the reaction is complete, the flexible loop opens to release the product. Janet Smith, of Purdue University, discusses these studies in an associated News and Views report. Serratia marcescens, which can be the cause of opportunistic infections in hospital patients, is able to use heme and hemoproteins as iron sources by mechanisms involving outer membrane heme-binding proteins and heme transport systems. HasA is secreted by S. marcescens under conditions of iron depletion and is essential for heme acquisition. Further studies of HasA together with HasR should lead to a more detailed understanding of the heme transfer mechanism by these pathogenic bacteria.
Prion proteins can adopt a certain three-dimensional shape that differs from that of a normal prion.
It is thought that these abnormal prions are infectious when ingested, that is, they somehow cause the host animal's own prion proteins to adopt the abnormal shape. Disease results when the abnormal prion shapes accumulate - protein plaques appear to form in the brain, and nerve cells degenerate. This prion shape change is similar, in concept, to a cylindrical balloon being twisted to make a new shape - the balloon itself has not changed in content, but it is adopting a new form. Many different types of experiments are ongoing to address how a prion molecule can adopt the normal and abnormal shapes. They demonstrate that the prion protein is one of the fastest folding proteins known - it can fold in under a millisecond.