Biology subjects

Houk, K. N.

Publications and source records attributed to Houk, K. N..

5 recordsLinked to original sources

bioRxiv2026

Biosynthetic allene and alkyne formation by enzymatic prenyl demethylation

Allenes and alkynes are versatile functional groups in total synthesis, medicinal chemistry, and bioorthogonal conjugation. The biosynthetic logic of how Nature installs allene or alkyne in natural products, especially that of allenes, is not well understood. Here we uncovered allenes and alkynes can be formed enzymatically through oxidative C(sp2)-demethylation of the common five-carbon prenyl group. Two fungal cytochrome P450 monooxygenases, PpnB and NseB, from the penipratynolene and sinuxylamide biosynthetic pathways, respectively, were shown to catalyze oxidative removal of a C(sp2)-methyl group in O-prenyl-L-tyrosine to afford O-homoallenyl-L-tyrosine and O-but-2-ynyl-L-tyrosine, respectively. Combining density functional theory calculations, heterologous expression, biotransformation and enzymatic assays with isotopically labeled substrates, a mechanism involving selective C-C bond cleavage followed by product-determining hydrogen atom abstraction is presented. An additional P450 enzyme from the penipratynolene pathway, PpnD, acts as an oxidative isomerase that converts the four-carbon terminal allene into a terminal alkyne. This unprecedented enzymatic editing strategy to install allene and alkyne expands the catalytic repertoire of P450 enzymes. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=100 SRC="FIGDIR/small/727785v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@54a57dorg.highwire.dtl.DTLVardef@13cb5d0org.highwire.dtl.DTLVardef@c4a2b7org.highwire.dtl.DTLVardef@196b357_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2024

Computational design of serine hydrolases

Enzymes that proceed through multistep reaction mechanisms often utilize complex, polar active sites positioned with sub-angstrom precision to mediate distinct chemical steps, which makes their de novo construction extremely challenging. We sought to overcome this challenge using the classic catalytic triad and oxyanion hole of serine hydrolases as a model system. We used RFdiffusion1 to generate proteins housing catalytic sites of increasing complexity and varying geometry, and a newly developed ensemble generation method called ChemNet to assess active site geometry and preorganization at each step of the reaction. Experimental characterization revealed novel serine hydrolases that catalyze ester hydrolysis with catalytic efficiencies (kcat/Km) up to 3.8 x 103 M-1 s-1, closely match the design models (C RMSDs < 1 [A]), and have folds distinct from natural serine hydrolases. In silico selection of designs based on active site preorganization across the reaction coordinate considerably increased success rates, enabling identification of new catalysts in screens of as few as 20 designs. Our de novo buildup approach provides insight into the geometric determinants of catalysis that complements what can be obtained from structural and mutational studies of native enzymes (in which catalytic group geometry and active site makeup cannot be so systematically varied), and provides a roadmap for the design of industrially relevant serine hydrolases and, more generally, for designing complex enzymes that catalyze multi-step transformations.

biochemistry↗

bioRxiv2019

Enzyme-free synthesis of natural phospholipids in water

All living organisms synthesize phospholipids as the primary constituent of their cell membranes. While phospholipids can spontaneously self-assemble in water to form membrane-bound vesicles, their aqueous synthesis requires pre-existing membrane-embedded enzymes. This limitation has led to models in which the first cells used simpler types of membrane building blocks and has hampered integration of phospholipid synthesis into artificial cells. Here we demonstrate that a combination of ion pairing and self-assembly of reactants allows high-yielding synthesis of cellular phospholipids in water. Acylation of 2-lysophospholipids using cationic thioesters occurs in mildly alkaline solutions resulting in the formation of cell-like membranes. A variety of membrane-forming natural phospholipids can be synthesized. Membrane formation takes place in water from natural alkaline sources, such as soda lakes and hydrothermal oceanic vents. When formed vesicles are transferred to more acidic solutions, electrochemical proton gradients are spontaneously established and maintained.

biochemistry↗

bioRxiv2018

Structural Basis for Stereoselective Dehydration and Hydrogen-Bonding Catalysis by the SAM-Dependent Pericyclase LepI

LepI is an S-adenosylmethionine (SAM)-dependent pericyclase that catalyzes the formation of 2-pyridone natural product leporin C. Biochemical characterization showed LepI can catalyze the stereoselective dehydration to yield a reactive (E)-quinone methide which can undergo a bifurcating intramolecular Diels-Alder (IMDA) and hetero-Diels-Alder (HDA) cyclization from an ambimodal transition state, and a [3,3]-retro-Claisen rearrangement to recycle the IMDA product into leporin C. Here we solved the X-ray crystal structures of SAM-bound LepI, and in complex with a substrate analog, the product leporin C, and a retro-Claisen reaction transition-state analog to understand the structural basis for the multitude of reactions. Structural and mutational analysis revealed how Nature evolves a classic methyltransferase active site into one that can serve as a dehydratase and a multifunctional pericyclase. Catalysis of both sets of reactions employ His133 and Arg295, two active site residues that are not found in canonical methyltransferases. An alternative role of SAM, which is not found to be in direct contact of the substrate, is also proposed.

biochemistry↗

bioRxiv2017

Structural basis of the Cope rearrangement and C-C bond-forming cascade in hapalindole/fischerindole biogenesis

STRUCTURESThe atomic coordinates and structure factors for:\n\nHpiC1 W73M/K132M SeMet (P212121) -1.7 [A]\n\nHpiC1 native (C2) -1.5 [A]\n\nHpiC1 native (P42) -2.1 [A]\n\nHpiC1 Y101F (C2) -1.4 [A]\n\nHpiC1 Y101S (C2) -1.4 [A]\n\nHpiC1 F138S (P21) -1.7 [A]\n\nHpiC1 Y101F/F138S (P21 -1.65 [A] have been deposited with the Research Collaboratory for Structural Bioinformatics as Protein Data Bank entries 5WPP, 5WPR, 6AL6, 5WPR, 5WPU, 6AL7, and 6AL8 (www.rcsb.org).\n\nGRANTSThis work was supported by: The authors thank the National Science Foundation under the CCI Center for Selective C-H Functionalization (CHE-1205646), the National Institutes of Health (CA70375 to RMW and DHS), R35 GM118101, R01 GM076477 and the Hans W. Vahlteich Professorship (to DHS) for financial support. M.G-B. thanks the Ramon Areces Foundation for a postdoctoral fellowship. J.N.S. acknowledges the support of the National Institute of General Medical Sciences of the National Institutes of Health under Award Number F32GM122218. Computational resources were provided by the UCLA Institute for Digital Research and Education (IDRE) and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF (OCI-1053575). The content does not necessarily represent the official views of the National Institutes of Health.\n\nABSTRACTHapalindole alkaloids are a structurally diverse class of cyanobacterial natural products defined by their varied polycyclic ring systems and diverse biological activities. These polycyclic scaffolds are generated from a common biosynthetic intermediate by the Stig cyclases in three mechanistic steps, including a rare Cope-rearrangement, 6-exo-trig cyclization, and electrophilic aromatic substitution. Here we report the structure of HpiC1, a Stig cyclase that catalyzes the formation of 12-epi-hapalindole U in vitro. The 1.5 [A] structure reveals a dimeric assembly with two calcium ions per monomer and the active sites located at the distal ends of the protein dimer. Mutational analysis and computational methods uncovered key residues for an acid catalyzed [3,3]-sigmatropic rearrangement and specific determinants that control the position of terminal electrophilic aromatic substitution leading to a switch from hapalindole to fischerindole alkaloids.

biochemistry↗