Hak Joong Kim

Targeted protein degradation (TPD) has been established as a viable alternative to attenuate the function of a specific protein of interest in both biological and clinical contexts. The unique TPD mode-of-action has allowed previously undruggable proteins to become feasible targets, expanding the landscape of "druggable" properties and "privileged" target proteins. As TPD continues to evolve, a range of innovative strategies, which do not depend on recruiting E3 ubiquitin ligases as in proteolys

Spinosyns are glycosylated polyketide-derived macrolides possessing a perhydro-as-indacene core that is presumably formed via a series of intramolecular cross-bridging reactions. The unusual structure of the spinosyn aglycone suggests an intriguing biosynthetic pathway for its formation, which is expected to be initiated by the oxidation of the 15-OH group of the mature polyketide precursor and may involve a Diels-Alder-type [4 + 2] cycloaddition reaction. Three possible routes, which differ in

Spinosyn A is a polyketide-derived macrolide produced by Saccharopolyspora spinosa and is an active ingredient in several commercial insecticides. It is glycosylated by a tri-O-methylated rhamnose at C-9 and a forosamine at C-17. Previous studies indicated that the rhamnose methyltransferases are encoded by the spnH, spnI, and spnK genes. To verify the functions of these methyltransferases and to study how they are coordinated to achieve the desired level of methylation of rhamnose, we studied t

Following the biosynthesis of polyketide backbones by polyketide synthases (PKSs), post-PKS modifications result in a significantly elevated level of structural complexity that renders the chemical synthesis of these natural products challenging. We report herein a total synthesis of the widely used polyketide insecticide spinosyn A by exploiting the prowess of both chemical and enzymatic methods. As more polyketide biosynthetic pathways are characterized, this chemoenzymatic approach is expecte

Covering: 1994 to 2019Owing to the rapid increase in nosocomial infections by antibiotic-resistant Acinetobacter baumannii and the paucity of effective treatment options for such infections, interest in the virulence factors involved in its successful dissemination and propagation in the human host have escalated in recent years. Acinetobacin, a siderophore of A. baumannii, is responsible for iron acquisition under nutritional depravation and has been shown to be one of the key virulence factors

The human pathogen Acinetobacter baumannii produces and utilizes acinetobactin for iron assimilation. Although two isomeric structures of acinetobactin, one featuring an oxazoline (Oxa) and the other with an isoxazolidinone (Isox) at the core, have been identified, their differential roles as virulence factors for successful infection have yet to be established. This study provides direct evidence that Oxa supplies iron more efficiently than Isox, primarily owing to its specific recognition by t

Total synthesis of anguibactin was accomplished for the first time, and the following biochemical characterizations allowed for the determination of its Fe(III) binding mode as well as the demonstration of its iron delivery capability for Acinetobacter baumannii. These properties, in addition to the thermal stability over acinetobactin, render anguibactin as a competent surrogate siderophore that can be useful for the future development of a siderophore-based antibiotic delivery system against A

Concerns about antibiotic-resistant Gram-negative pathogens are escalating, and accordingly siderophore-based intracellular antibiotic delivery is attracting more attention as an effective means to overcome these infections. Despite the successful clinical translation of this strategy, the delivery potential of siderophores has been limited to periplasm targeting, and this has appreciably restricted the repertoire of applicable antibiotics. To overcome this shortcoming of the current technology,

The stereoselective synthesis of fimsbactin A, a siderophore of the human pathogen <i>Acinetobacter baumannii</i>, was established. Based on this synthetic route, various fimsbactin stereoisomeric analogues were generated and tested for their iron delivery activity for <i>A. baumannii</i>. This investigation revealed that the fimsbactin uptake machinery in this bacterium was indeed highly stereoselective in substrate recognition.

The ability of fimsbactin B, a natural siderophore of <i>Acinetobacter baumannii</i>, to function as an antibiotic delivery vehicle was investigated by synthesizing three structurally diversified fimsbactin B-cefaclor conjugates. Their antimicrobial activities were <i>Acinetobacter</i>-selective and up to 128-fold more potent than that of cefaclor alone. This activity enhancement originated from the fimsbactin-B-dependent active uptake of cefaclor. Thus, fimsbactin-B-based antibiotic delivery ca

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Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A novel fluorescence probe capable of assessing the cytoplasmic entry of siderophore-based conjugates was synthesized and evaluated by photochemical characterization and cell-based assays. The specific responsiveness to the cytoplasmic entry of the probe was implemented by adopting a disulfide linker, whose cleavage under the reducing conditions of the cytoplasm induced the display of a distinctive fluorescence signal.