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6,907 results on '"Lee, Seung Hwan"'

7. Revealing reaction intermediates in one-carbon elongation by thiamine diphosphate/CoA-dependent enzyme family

Author

Kim, Youngchang, Lee, Seung Hwan, Gade, Priyanka, Nattermann, Maren, Maltseva, Natalia, Endres, Michael, Chen, Jing, Wichmann, Philipp, Hu, Yang, Marchal, Daniel G, Yoshikuni, Yasuo, Erb, Tobias J, Gonzalez, Ramon, Michalska, Karolina, and Joachimiak, Andrzej

Subjects
Chemical Sciences, Chemical sciences
Abstract

2-Hydroxyacyl-CoA lyase/synthase (HACL/S) is a thiamine diphosphate (ThDP)-dependent versatile enzyme originally discovered in the mammalian α-oxidation pathway. HACL/S natively cleaves 2-hydroxyacyl-CoAs and, in its reverse direction, condenses formyl-CoA with aldehydes or ketones. The one-carbon elongation biochemistry based on HACL/S has enabled the use of molecules derived from greenhouse gases as biomanufacturing feedstocks. We investigated several HACL/S family members with high activity in the condensation of formyl-CoA and aldehydes, and distinct chain-length specificities and kinetic parameters. Our analysis revealed the structures of enzymes in complex with acyl-CoA substrates and products, several covalent intermediates, bound ThDP and ADP, as well as the C-terminal active site region. One of these observed states corresponds to the intermediary α-carbanion with hydroxymethyl-CoA covalently attached to ThDP. This research distinguishes HACL/S from related sub-families and identifies key residues involved in substrate binding and catalysis. These findings expand our knowledge of acyloin-condensation biochemistry and offer attractive prospects for biocatalysis using carbon elongation.

Published
2024

39. Characteristics of cellulose nanofibril films prepared by liquid- and gas-phase esterification processes

Author

Kim Jeong-Ki, Bandi Rajkumar, Dadigala Ramakrishna, Han Song-Yi, Van Hai Le, Cho Seung-Woo, Ma Seo-Young, Lee Da-Young, Kwon Gu-Joong, and Lee Seung-Hwan

Subjects
nanocellulose, fatty acid chlorides, hydrophobicity, tensile properties, crystallinity, Polymers and polymer manufacture, TP1080-1185
Abstract

Cellulose nanofibrils (CNFs) are versatile materials, but their sensitivity to humidity affects performance. Esterification with fatty acids enhances the hydrophobicity of CNF films. This study compared gas- and liquid-phase esterification using three fatty acid chlorides at different dosages. Gas-phase esterification minimally affected cellulose crystallinity, maintaining a crystallinity index exceeding 55.8%, whereas liquid-phase esterification significantly reduced crystallinity. Gas-phase esterification achieved hydrophobicity (water contact angle >100°) with less fatty acid chlorides (0.50 eq/OH) compared to liquid-phase esterification (1.00 eq/OH). Tensile strength significantly dropped in the liquid phase (68.4–6 MPa) and up to an 8-fold decrease in the elastic modulus. Conversely, gas-phase esterification maintained tensile strength over 40 MPa, and elastic modulus increased by a minimum of 2.5 times. However, gas-phase esterification resulted in a 5-fold reduction in elongation at break (%). Thermogravimetric analysis indicated a high T max of 362°C for liquid-phase esterified samples and a substantial 24.9% residual weight for gas-phase esterified samples.

Published
2024
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