Tribulus terrestris fruits are well known for their usage in pharmaceutical preparations and food supplements. The methanol extract of T. terrestris fruits showed potent inhibition against the papain-like protease (PLpro), an essential proteolylic enzyme for protection to pathogenic virus and bacteria. Subsequent bioactivity-guided fractionation of this extract led to six cinnamic amides (1-6) and ferulic acid (7). Compound 6 emerged as new compound possessing the very rare carbinolamide motif. These compounds (1-7) were evaluated for severe acute respiratory syndrome coronavirus (SARS-CoV) PLpro inhibitory activity to identify their potencies and kinetic behavior. Compounds (1-6) displayed significant inhibitory activity with IC 50 values in the range 15.8-70.1 µM. The new cinnamic amide 6 was found to be most potent inhibitor with an IC 50 of 15.8 µM. In kinetic studies, all inhibitors exhibited mixed type inhibition. Furthermore, the most active PLpro inhibitors (1-6) were proven to be present in the native fruits in high quantities by HPLC chromatogram and liquid chromatography with diode array detection and electrospray ionization mass spectrometry (LC-DAD-ESI/MS).

Bacterial RNA polymerase employs extra-cytoplasmic function (ECF) σ factors to regulate context-specific gene expression programs. Despite being the most abundant and divergent σ factor class, the structural basis of ECF σ factor-mediated transcription initiation remains unknown. Here, we determine a crystal structure of Mycobacterium tuberculosis (Mtb) RNAP holoenzyme comprising an RNAP core enzyme and the ECF σ factor σH (σH-RNAP) at 2.7 Å, and solve another crystal structure of a transcription initiation complex of Mtb σH-RNAP (σH-RPo) comprising promoter DNA and an RNA primer at 2.8 Å. The two structures together reveal the interactions between σH and RNAP that are essential for σH-RNAP holoenzyme assembly as well as the interactions between σH-RNAP and promoter DNA responsible for stringent promoter recognition and for promoter unwinding. Our study establishes that ECF σ factors and primary σ factors employ distinct mechanisms for promoter recognition and for promoter unwinding.

Neurofibrillary tangles (NFTs) represent products of insoluble tau protein in the brains of patients with Alzheimer disease (AD). The cerebrospinal fluid (CSF) tau level is a biomarker in AD diagnosis. The soluble portion of tau protein in brain parenchyma is presumably the source for CSF tau but this has not previously been quantified. We measured CSF tau and soluble brain tau at autopsy in temporal and frontal brain tissue samples from 7 cognitive normal, 12 mild cognitively impaired, and 19 AD subjects. Based on the measured brain soluble tau, we calculated the whole brain tau load and estimated tau secretion factor. Our results suggest that the increase in NFT in AD is likely attributable to post-translational processes; the increase in CSF tau in AD patients is due to an accelerated carrier-based secretion. Moreover, cognitive dysfunction assessed by final Mini-Mental State Examination scores correlated with the secretion factor but not with the soluble tau.