Biomedical subjects

Martin Mense

Publications and source records attributed to Martin Mense.

3 recordsLinked to original sources

PubMed2025

A streamlined base editor engineering strategy to reduce bystander editing.

Base editing (BE) can permanently correct over half of known human pathogenic genetic variants without requiring a repair template, thus serving as a promising therapeutic tool to treat a broad spectrum of genetic diseases. However, the broad activity windows of current base editors pose a major challenge to their therapeutic application. Here, we show that integrating a naturally occurring oligonucleotide binding module into the deaminase active center of TadA-8e, a highly active deoxyadenosine deaminase, enhances its editing specificity. When conjugated with a Cas9 nickase or alternative PAM Cas9 variants, the engineered TadA variant-TadA-NW1-consistently achieves robust A-to-G editing efficiencies within an editing window consisting of four nucleotides, substantially narrower than the 10-bp editing window of the TadA-8e-derived ABEs. Moreover, compared to ABE8e, ABE-NW1 shows significantly decreased Cas9-dependent and -independent off-target activity while maintaining similar on-target editing efficiency. Further, TadA-NW1 can be reprogrammed to perform desired cytidine deamination and adenine transversion within a restricted editing window. Finally, in a cystic fibrosis (CF) cell model, ABE-NW1 outperforms existing ABEs in accurately and efficiently correcting the CFTR W1282X variant, one of the most common CF-causing mutations. In all, we engineered a suite of base editors with refined activity windows, enabling more precise base editing. Importantly, this study presents a streamlined genome editor re-engineering strategy to accelerate the development of therapeutic base editing.

Gene Editing↗

PubMed2006

In vivo phosphorylation of CFTR promotes formation of a nucleotide-binding domain heterodimer.

The human ATP-binding cassette (ABC) protein CFTR (cystic fibrosis transmembrane conductance regulator) is a chloride channel, whose dysfunction causes cystic fibrosis. To gain structural insight into the dynamic interaction between CFTR's nucleotide-binding domains (NBDs) proposed to underlie channel gating, we introduced target cysteines into the NBDs, expressed the channels in Xenopus oocytes, and used in vivo sulfhydryl-specific crosslinking to directly examine the cysteines' proximity. We tested five cysteine pairs, each comprising one introduced cysteine in the NH(2)-terminal NBD1 and another in the COOH-terminal NBD2. Identification of crosslinked product was facilitated by co-expression of NH(2)-terminal and COOH-terminal CFTR half channels each containing one NBD. The COOH-terminal half channel lacked all native cysteines. None of CFTR's 18 native cysteines was found essential for wild type-like, phosphorylation- and ATP-dependent, channel gating. The observed crosslinks demonstrate that NBD1 and NBD2 interact in a head-to-tail configuration analogous to that in homodimeric crystal structures of nucleotide-bound prokaryotic NBDs. CFTR phosphorylation by PKA strongly promoted both crosslinking and opening of the split channels, firmly linking head-to-tail NBD1-NBD2 association to channel opening.

Animals↗

PubMed2002

Extracellular domains, transmembrane segments, and intracellular domains interact to determine the cation selectivity of Na,K- and gastric H,K-ATPase.

We have previously reported that three residues of the fourth transmembrane segment (TM4) of the Na,K- and gastric H,K-ATPase alpha-subunits appear to play a major role in the distinct cation selectivities of these pumps [Mense, M., et al. (2000) J. Biol. Chem. 275, 1749-1756]. Substituting these three residues in the Na,K-ATPase sequence with their H,K-ATPase counterparts (L319F, N326Y, T340S) and replacing the TM3-TM4 ectodomain sequence with that of the H,K-ATPase alpha-subunit result in a pump that exhibits 50% of its maximal ATPase activity in the absence of Na(+) when the assay is performed at pH 6.0. This effect is not seen when the ectodomain alone is replaced. To gain more insight into the contributions of the three residues to establishing the selectivity of these pumps for Na(+) ions versus protons, we generated Na,K-ATPase constructs in which these residues are replaced by their H,K-ATPase counterparts either singly or in combinations. Surprisingly, none of the point mutants nor even the triple mutant was able to hydrolyze ATP at pH 6.0 at a rate greater than 20% of their respective V(max)s. For the point mutants L319F and N326Y, protons seem to competitively inhibit ATP hydrolysis at pH 6.0, based on the low apparent affinity for Na(+) ions at pH 6.0 compared to pH 7.5. It would appear, therefore, that the cation selectivity of Na,K- and H,K-ATPase is generated through a cooperative effort between residues of transmembrane segments and the flanking loops that connect these transmembrane domains. This view is further supported by homology modeling of the Na,K-ATPase based on the crystal structure of the SERCA pump.

Animals↗