Structural basis of CD4 downregulation by HIV-1 Nef.

The HIV-1 Nef protein suppresses multiple immune surveillance mechanisms to promote viral pathogenesis and is an attractive target for the development of novel therapeutics. A key function of Nef is to remove the CD4 receptor from the cell surface by hijacking clathrin- and adaptor protein complex 2 (AP2)-dependent endocytosis. However, exactly how Nef does this has been elusive. Here, we describe the underlying mechanism as revealed by a 3.0-Å crystal structure of a fusion protein comprising Nef and the cytoplasmic domain of CD4 bound to the tetrameric AP2 complex. An intricate combination of conformational changes occurs in both Nef and AP2 to enable CD4 binding and downregulation. A pocket on Nef previously identified as crucial for recruiting class I MHC is also responsible for recruiting CD4, revealing a potential approach to inhibit two of Nef's activities and sensitize the virus to immune clearance.

Prepared endotracheal tubes: are they a potential source for pathogenic microorganisms?

UNLABELLED: Prepared endotracheal tubes (PETTs) are frequently used for unanticipated difficult intubation, but their storage time is highly variable and institution-dependent. We sought to determine first, if open, unused PETTs are a potential source of pathogenic microorganisms, and second, if PETTs can provide a medium for bacterial survival after deliberate contamination. A stylet was inserted into a 7-mm ETT, and this system was ethylene oxide sterilized. The PETTs were placed in 20 different locations and sampled 8 times in a 4-wk period. Growth was determined after 48-h incubation, and the microorganism was identified. In Phase 2, the PETT (n = 40) was swabbed with a fresh suspension of H. influenzae, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecium, or a negative control. Nonvirulent bacteria were cultured from 13 of 160 (8.1%) samples and from 15 of 320 (4.7%) samples in Phases 1 and 2, respectively. No PETT grew the same bacteria more than once. In Phase 2, after 24 h, only E. faecium was recovered. Based on this study, the pathogenic potential of PETTs is very small, and they can be safely used for up to 1 mo. This practice could translate to significant cost reduction for operating room budgets. IMPLICATIONS: Prepared endotracheal tubes (PETTs) are back-up airway equipment to be used in the case of a difficult intubation. A short PETT shelf life because of unknown safe storage time results in significant budget costs. This blinded, controlled study examined the pathogenic potential of PETTs in the operating room environment.