No abstract

MELK (maternal embryonic leucine zipper kinase), which is a member of the AMPK (AMP-activated protein kinase)-related kinase family, plays important roles in diverse cellular processes and has become a promising drug target for certain cancers. However, the regulatory mechanism of MELK remains elusive. Here, we report the crystal structure of a fragment of human MELK that contains the kinase domain and ubiquitin-associated (UBA) domain. The UBA domain tightly binds to the back of the kinase domain, which may contribute to the proper conformation and activity of the kinase domain. Interestingly, the activation segment in the kinase domain displays a unique conformation that contains an intramolecular disulfide bond. The structural and biochemical analyses unravel the molecular mechanisms for the autophosphorylation/activation of MELK and the dependence of its catalytic activity on reducing agents. Thus, our results may provide the basis for designing specific MELK inhibitors for cancer treatment.

PDB reference: p202 HINa domain, 4lnqThe HIN-200 family of proteins play significant roles in inflammation-related processes. Among them, AIM2 (absent in melanoma 2) and IFI16 ( -interferoninducible protein 16) recognize double-stranded DNA to initiate inflammatory responses. In contrast, p202, a mouse interferon-inducible protein containing two HIN domains (HINa and HINb), has been reported to inhibit Aim2-mediated inflammatory signalling in mouse. To understand the inhibitory mechanism, the crystal structure of the p202 HINa domain in complex with a 20 bp DNA was determined, in which p202 HINa nonspecifically recognizes both strands of DNA through electrostatic attraction. The p202 HINa domain binds DNA more tightly than does AIM2 HIN, and the DNA-binding mode of p202 HINa is different from that of the AIM2 HIN and IFI16 HINb domains. These results, together with the reported data on p202 HINb, lead to an interaction model for full-length p202 and dsDNA which provides a conceivable mechanism for the negative regulation of Aim2 inflammasome activation by p202.