The granulocyte colony‐stimulating factor (G‐CSF) receptor has a composite structure consisting of an immunoglobulin(Ig)‐like domain, a cytokine receptor‐homologous (CRH) domain and three fibronectin type III (FNIII) domains in the extracellular region. Introduction of G‐CSF receptor cDNA into IL‐3‐dependent murine myeloid cell line FDC‐P1 and pro‐B cell line BAF‐B03, which normally do not respond to G‐CSF, enabled them to proliferate in response to G‐CSF. On the other hand, expression of the G‐CSF receptor cDNA in the IL‐2‐dependent T cell line CTLL‐2 did not enable it to grow in response to G‐CSF, although G‐CSF could transiently stimulate DNA synthesis. Mutational analyses of the G‐CSF receptor in FDC‐P1 cells indicated that the N‐terminal half of the CRH domain was essential for the recognition of G‐CSF, but the Ig‐like, FNIII and cytoplasmic domains were not. The CRH domain and a portion of the cytoplasmic domain of about 100 amino acids in length were indispensable for transduction of the G‐CSF‐triggered growth signal.
In
Pseudomonas aeruginosa
, MexAB–OprM plays a central role in multidrug resistance by ejecting various drug compounds, which is one of the causes of serious nosocomial infections. Although the structures of the components of MexAB–OprM have been solved individually by X-ray crystallography, no structural information for fully assembled pumps from
P. aeruginosa
were previously available. In this study, we present the structure of wild-type MexAB–OprM in the presence or absence of drugs at near-atomic resolution. The structure reveals that OprM does not interact with MexB directly, and that it opens its periplasmic gate by forming a complex. Furthermore, we confirm the residues essential for complex formation and observed a movement of the drug entrance gate. Based on these results, we propose mechanisms for complex formation and drug efflux.
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