Biology subjects

Han, J. I.

Publications and source records attributed to Han, J. I..

3 recordsLinked to original sources

bioRxiv2026

Mitochondrial phosphate carrier-dependence of mitochondrial calcium chelation and respiration in skeletal muscle

The past decade has seen remarkable progress in the molecular resolution of the influx and efflux components of mitochondrial Ca2+ handling, but little progress in matrix Ca2+ chelation that is central to mitochondrial calcium signaling. Among possible chelators, inorganic phosphate (Pi) is dynamic, and its uptake can lessen during Ca2+ uptake the rundown of the membrane potential, the primary driving force for Ca2+ uptake. Thus, PiC, the major mitochondrial Pi transporter, is well-positioned to regulate mitochondrial Ca2+ handling. To test this, we depleted (KD) PiC in murine skeletal muscle. We show that PiC depletion enhances the matrix free Ca2+ rise across a range of Ca2+ uptake activities, and surprisingly, causes elevated mitochondrial Ca2+ uptake, which seems to arise from an increased abundance of the mitochondrial Ca2+ uniporter. With protein levels of non-mitochondrial Ca2+ handling proteins unaltered, the greater mitochondrial Ca2+ uptake may drive a suppressed cytoplasmic Ca2+ response to tetanic stimulation, via lesser Ca2+-mediated positive feedback on Ca2+ release channels, contributing to an exercise deficit in KD mice. Alternatively, less buffering of matrix Ca2+ might be beneficial. We test these possibilities by lowering MCU, the uniporters pore forming subunit, in skeletal muscle of adult PiC KD mice, and find a worsened exercise deficit. This study establishes the requirement for PiC to maintain a bound fraction of Ca2+ in the matrix, and reveals a fitness benefit for elevated [Ca2+]m in striated muscle depleted of PiC.

biochemistry↗

bioRxiv2023

Acyl-CoA thioesterase-2 facilitates beta-oxidation in glycolytic skeletal muscle in a lipid supply dependent manner

Acyl-Coenzyme A (acyl-CoA) thioesters are compartmentalized intermediates that participate in in multiple metabolic reactions within the mitochondrial matrix. The limited availability of free CoA (CoASH) in the matrix raises the question of how the local acyl-CoA concentration is regulated to prevent trapping of CoASH from overload of any specific substrate. Acyl-CoA thioesterase-2 (ACOT2) hydrolyzes long-chain acyl-CoAs to their constituent fatty acids and CoASH, and is the only mitochondrial matrix ACOT refractory to inhibition by CoASH. Thus, we reasoned that ACOT2 may constitutively regulate matrix acyl-CoA levels. Acot2 deletion in murine skeletal muscle (SM) resulted in acyl-CoA build-up when lipid supply and energy demands were modest. When energy demand and pyruvate availability were elevated, lack of ACOT2 activity promoted glucose oxidation. This preference for glucose over fatty acid oxidation was recapitulated in C2C12 myotubes with acute depletion of Acot2, and overt inhibition of {beta}-oxidation was demonstrated in isolated mitochondria from Acot2-depleted glycolytic SM. In mice fed a high fat diet, ACOT2 enabled the accretion of acyl-CoAs and ceramide derivatives in glycolytic SM, and this was associated with worse glucose homeostasis compared to when ACOT2 was absent. These observations suggest that ACOT2 supports CoASH availability to facilitate {beta}-oxidation in glycolytic SM when lipid supply is modest. However, when lipid supply is high, ACOT2 enables acyl-CoA and lipid accumulation, CoASH sequestration, and poor glucose homeostasis. Thus, ACOT2 regulates matrix acyl-CoA concentration in glycolytic muscle, and its impact depends on lipid supply.

biochemistry↗

bioRxiv2018

Refinement of highly flexible protein structures using simulation-guided spectroscopy

Highly flexible proteins present a special challenge for structure determination because they are multi-structured yet not disordered, and the resulting conformational ensembles are essential for understanding function. Determining such ensembles is difficult because many measurements that capture multiple conformational populations provide sparse data. A powerful opportunity exists to leverage molecular simulations for spectroscopic experiment selection. We have developed an information-theoretic approach to guide experiments by identifying which measurements best refine the underlying conformational ensemble. We have tested this approach on three flexible bacterial proteins. For proteins where a clear mechanistic hypothesis drives label selection, our approach systematically identifies labels that would test this hypothesis. Furthermore, when available data do not yield an obvious mechanistically-guided label selection strategy, our approach guides label selection and produces conformational refinement that significantly outperforms standard structure-guided approaches. Our information-theoretic approach to label selection thus offers a particular advantage when refining challenging, underdetermined protein conformational ensembles.

bioinformatics↗