1. The "tale" of poly(A) binding protein: the MLLE domain and PAM2-containing proteins
Jingwei Xie, Guennadi Kozlov, Kalle Gehring Biochim Biophys Acta. 2014 Nov;1839(11):1062-8. doi: 10.1016/j.bbagrm.2014.08.001. Epub 2014 Aug 10.
The cytoplasmic poly(A) binding protein 1 (PABPC1) is an essential eukaryotic translational initiation factor first described over 40 years ago. Most studies of PABPC1 have focused on its N-terminal RRM domains, which bind the mRNA 3' poly(A) tail and 5' translation complex eIF4F via eIF4G; however, the protein also contains a C-terminal MLLE domain that binds a peptide motif, termed PAM2, found in many proteins involved in translation regulation and mRNA metabolism. Studies over the past decade have revealed additional functions of PAM2-containing proteins (PACs) in neurodegenerative diseases, circadian rhythms, innate defense, and ubiquitin-mediated protein degradation. Here, we summarize functional and structural studies of the MLLE/PAM2 interaction and discuss the diverse roles of PACs.
2. Engineered CRISPR-Cas12a variants with increased activities and improved targeting ranges for gene, epigenetic and base editing
Benjamin P Kleinstiver, et al. Nat Biotechnol. 2019 Mar;37(3):276-282. doi: 10.1038/s41587-018-0011-0. Epub 2019 Feb 11.
Broad use of CRISPR-Cas12a (formerly Cpf1) nucleases1 has been hindered by the requirement for an extended TTTV protospacer adjacent motif (PAM)2. To address this limitation, we engineered an enhanced Acidaminococcus sp. Cas12a variant (enAsCas12a) that has a substantially expanded targeting range, enabling targeting of many previously inaccessible PAMs. On average, enAsCas12a exhibits a twofold higher genome editing activity on sites with canonical TTTV PAMs compared to wild-type AsCas12a, and we successfully grafted a subset of mutations from enAsCas12a onto other previously described AsCas12a variants3 to enhance their activities. enAsCas12a improves the efficiency of multiplex gene editing, endogenous gene activation and C-to-T base editing, and we engineered a high-fidelity version of enAsCas12a (enAsCas12a-HF1) to reduce off-target effects. Both enAsCas12a and enAsCas12a-HF1 function in HEK293T and primary human T cells when delivered as ribonucleoprotein (RNP) complexes. Collectively, enAsCas12a provides an optimized version of Cas12a that should enable wider application of Cas12a enzymes for gene and epigenetic editing.
3. Pam2 lipopeptides enhance the immunosuppressive activity of monocytic myeloid-derived suppressor cells by STAT3 signal in chronic inflammation
Xiaoxia Zhan, Xiaobing Jiang, Qiuying He, Liangyin Zhong, Yichong Wang, Yulan Huang, Shitong He, Junli Sheng, Jianwei Liao, Zhijie Zeng, Shengfeng Hu Cent Eur J Immunol. 2022;47(1):30-40. doi: 10.5114/ceji.2022.113086. Epub 2022 Feb 11.
Chronic inflammation develops when the immune system is unable to clear a persistent insult. Unresolved chronic inflammation leads to immunosuppression to maintain the internal homeostatic conditions, which is mediated primarily by myeloid-derived suppressor cells (MDSCs). Toll-like receptors 2 (TLR2) has an important role in chronic inflammation and can be activated by a vast number and diversity of TLR2 ligands, for example Pam2CSK4. However, the regulatory effect of TLR2 signaling on MDSCs in chronic inflammation remains controversial. This study demonstrated that heat-killed Mycobacterium bovis BCG-induced pathology-free chronic inflammation triggered suppressive monocytic MDSCs (M-MDSCs) that expressed TLR2. Activation of TLR2 signaling by Pam2CSK4 treatment enhanced immunosuppression of M-MDSCs by upregulating inducible nitric oxide synthase (iNOS) activity and nitric oxide (NO) production partly through signal transducer and activator of transcription 3 (STAT3) activation. Thus, TLR2 has a fundamental role in promoting the MDSC-mediated immunosuppressive environment during chronic inflammation and might represent a potentially therapeutic target in chronic inflammation disease.
