About

Anant Menon, Ph.D., is a Professor of Biochemistry and Biophysics at Weill Cornell Medicine. His laboratory is focused on fundamental aspects of cellular membrane biogenesis, investigating processes related to lipid biosynthesis, the propagation of the phospholipid bilayer of biological membranes, translocation (flip-flop) of lipids across bilayers, and intracellular lipid transport. The lab employs biochemical, biophysical, genetic, and chemical methods to approach these problems, contributing to a deeper understanding of membrane biology and lipid dynamics.

Research topics

• Biology
• Cell biology
• Biochemistry
• Chemistry
• Biophysics
• Materials science
• Computational biology
• Evolutionary biology
• Cognitive science
• Botany

Selected publications

• Regulation of phospholipid scramblases by cholesterol

  Methods in enzymology on CD-ROM/Methods in enzymology · 2026-01-01

  book-chapterSenior author
  PublisherDOI

• A pyrophosphatase that regulates lipid precursors of <i>N</i>-glycosylation

  The Journal of Cell Biology · 2025-10-10

  articleOpen access1st authorCorresponding

  The oligosaccharide used for protein N-glycosylation in the ER is built as a glycolipid. A recent study by Li, Suzuki, and colleagues (https://doi.org/10.1083/jcb.202501239) identifies a long-sought enzyme that hydrolyzes this lipid as part of a possible homeostatic/quality control mechanism.

  PublisherOA PDFDOI

• A single vesicle fluorescence microscopy platform to quantify phospholipid scrambling

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-04-23

  preprintOpen accessCorresponding

  Scramblases play important roles in physiology by translocating phospholipids bidirectionally across cell membranes. For example, scrambling facilitated by dimers of the Voltage-Dependent Anion Channel 1 (VDAC1) enables endoplasmic reticulum-derived phospholipids to cross the outer membrane to enter mitochondria. Precise quantification of lipid scrambling, while critical for mechanistic understanding, cannot be obtained from ensemble averaged measurements of reconstituted scramblases. Here, we describe a microscopy platform for high-throughput imaging of single vesicles reconstituted with fluorescently labeled phospholipids and heterogeneously crosslinked VDAC1 dimers. For each vesicle, we quantify size, protein occupancy and scrambling rate. Notably, we find that individual VDAC1 dimers have different activities, ranging from <100 to >10,000 lipids per second. This kinetic heterogeneity, masked in ensemble measurements, reveals that only some dimer interfaces are capable of promoting rapid scrambling, as suggested by molecular dynamics simulations. We extend our analyses to opsin, a monomeric G protein-coupled receptor scramblase, thereby demonstrating the versatility of our platform for quantifying transbilayer lipid transport and exploring its regulation.

  PublisherOA PDFDOI

• Opsins are Phospholipid Scramblases in All Domains of Life

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-08-18

  preprintOpen access

  Abstract Opsins are highly abundant retinal proteins in the membranes of photoheterotrophic bacteria. However, some microbial genomes encode an opsin but lack the gene for the final enzyme in retinal synthesis. To account for this paradox, we hypothesized that bacterial opsins play a role in membrane structure and/or biogenesis independent from their potential for light-driven signaling or proton pumping. After purifying actinorhodopsin from a cell-free expression system and from E. coli membranes upon overexpression, we demonstrated both in vitro and in silico that actinorhodopsin from Nanopelagicus ca. is a phospholipid scramblase, serving in its pentameric state as a retinal-independent phospholipid diffusion channel. Phospholipid headgroups move along a transbilayer path between actinorhodopsin protomers, to equilibrate lipid content in the inner and outer leaflets. Two profound activities, membrane biosynthesis and capture of light energy, are thus facilitated by one ancient bacterial polypeptide. Light-dependent activity and light-independent phospholipid scrambling are shared functions of eukaryotic, archaeal, and bacterial rhodopsins. Importance Cells are surrounded by membranes which concentrate metabolites and protect cellular contents. Most biomembranes are phospholipid bilayers, in which the phospholipids of each leaflet orient their greasy tails inward and polar groups outward. Bilayer biogenesis depends on phospholipids synthesized on the cytofacial side of the membrane reorienting to the extracellular membrane leaflet. This reorientation requires proteins, termed scramblases, and it was shown that rhodopsins –– 7-helix photoactive membrane proteins bound to the cofactor retinal –– from organisms as widely divergent as mammals and archaea possess scramblase activity. Now we conclusively demonstrate using purified proteins in laboratory membranes as well as computational approaches, that bacterial rhodopsins are also phospholipid scramblases. This work is important because it highlights a surprising commonality among bacteria, archaea and eukaryotes and because it shows that rhodopsins – ancient proteins found in the last universal common ancestor – manifest two seemingly unrelated biochemical functions in one protein.

  PublisherOA PDFDOI

• One-Pot Reconstitution of GPCRs into Unilamellar Vesicles for Fluorescence-Based Phospholipid Scramblase Activity Assay

  Methods in molecular biology · 2025-01-01 · 2 citations

  articleSenior author
  PublisherDOI

• Opsins are phospholipid scramblases in all domains of life

  mBio · 2025-11-26 · 1 citations

  articleOpen access

  ABSTRACT Opsins are highly abundant retinal proteins in the membranes of photoheterotrophic bacteria. However, some microbial genomes encode an opsin but lack the gene for the final enzyme in retinal synthesis. To account for this paradox, we hypothesized that bacterial opsins play a role in membrane structure and/or biogenesis independent of their potential for light-driven signaling or proton pumping. After purifying actinorhodopsin from a cell-free expression system and from Escherichia coli membranes upon overexpression, we demonstrated both in vitro and in silico that actinorhodopsin from Nanopelagicus ca . is a phospholipid scramblase, serving in its pentameric state as a retinal-independent phospholipid diffusion channel. Phospholipid headgroups move along a transbilayer path between actinorhodopsin protomers to equilibrate lipid content in the inner and outer leaflets. Two profound activities, membrane biosynthesis and capture of light energy, are thus facilitated by one ancient bacterial polypeptide. Light-dependent activity and light-independent phospholipid scrambling are shared functions of eukaryotic, archaeal, and bacterial rhodopsins. IMPORTANCE Cells are surrounded by membranes that concentrate metabolites and protect cellular contents. Most biomembranes are phospholipid bilayers, in which the phospholipids of each leaflet orient their greasy tails inward and polar groups outward. Bilayer biogenesis depends on phospholipids synthesized on the cytofacial side of the membrane reorienting to the extracellular membrane leaflet. This reorientation requires proteins, termed scramblases, and it was shown that rhodopsins—7-helix photoactive membrane proteins bound to the cofactor retinal—from organisms as widely divergent as mammals and archaea possess scramblase activity. Now we conclusively demonstrate, using purified proteins in laboratory membranes as well as computational approaches, that bacterial rhodopsins are also phospholipid scramblases. This work is important because it highlights a surprising commonality among bacteria, archaea, and eukaryotes and because it shows that rhodopsins—ancient proteins found in the last universal common ancestor—manifest two seemingly unrelated biochemical functions in one protein.

  PublisherDOI

• Protocol for the production and reconstitution of VDAC1 for functional assays

  STAR Protocols · 2024-08-09 · 9 citations

  articleOpen accessCorresponding

  The voltage-dependent anion channel (VDAC) is an abundant and multifunctional outer mitochondrial membrane protein, playing key roles in neurodegeneration, apoptosis, and mitochondrial membrane biogenesis. Here, we present a protocol to produce and reconstitute high yields of detergent-solubilized VDAC, expressed as inclusion bodies in E. coli . We describe steps for purification by affinity chromatography and refolding in lauryldimethylamine-N-oxide (LDAO). We then detail procedures for reconstituting VDAC into membrane vesicles to assay its channel and phospholipid scramblase activity via fluorescence-based assays. For complete details on the use and execution of this protocol, please refer to Bergdoll et al., 1 Queralt-Martín et al., 2 and Jahn et al. 3 • Expression of VDAC1 in E. coli and purification in urea • Detailed description of protein folding in LDAO • Step-by-step details of VDAC1 cross-linking and reconstitution into liposomes • Fluorescence-based assay of VDAC channel and scramblase activity Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics. The voltage-dependent anion channel (VDAC) is an abundant and multifunctional outer mitochondrial membrane protein, playing key roles in neurodegeneration, apoptosis, and mitochondrial membrane biogenesis. Here, we present a protocol to produce and reconstitute high yields of detergent-solubilized VDAC, expressed as inclusion bodies in E. coli . We describe steps for purification by affinity chromatography and refolding in lauryldimethylamine-N-oxide (LDAO). We then detail procedures for reconstituting VDAC into membrane vesicles to assay its channel and phospholipid scramblase activity via fluorescence-based assays.

  PublisherOA PDFDOI

• A cholesterol switch controls phospholipid scrambling by G protein–coupled receptors

  Journal of Biological Chemistry · 2024-01-16 · 24 citations

  articleOpen accessSenior authorCorresponding

  Class A G protein-coupled receptors (GPCRs), a superfamily of cell membrane signaling receptors, moonlight as constitutively active phospholipid scramblases. The plasma membrane of metazoan cells is replete with GPCRs yet has a strong resting trans-bilayer phospholipid asymmetry, with the signaling lipid phosphatidylserine confined to the cytoplasmic leaflet. To account for the persistence of this lipid asymmetry in the presence of GPCR scramblases, we hypothesized that GPCR-mediated lipid scrambling is regulated by cholesterol, a major constituent of the plasma membrane. We now present a technique whereby synthetic vesicles reconstituted with GPCRs can be supplemented with cholesterol to a level similar to that of the plasma membrane and show that the scramblase activity of two prototypical GPCRs, opsin and the β1-adrenergic receptor, is impaired upon cholesterol loading. Our data suggest that cholesterol acts as a switch, inhibiting scrambling above a receptor-specific threshold concentration to disable GPCR scramblases at the plasma membrane.

  PublisherOA PDFDOI

• Molecular characterization of Rft1, an ER membrane protein associated with congenital disorder of glycosylation RFT1-CDG

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-04-03 · 1 citations

  preprintOpen accessSenior authorCorresponding

  ABSTRACT The oligosaccharide needed for protein N -glycosylation is assembled on a lipid carrier via a multi-step pathway. Synthesis is initiated on the cytoplasmic face of the endoplasmic reticulum (ER) and completed on the luminal side after transbilayer translocation of a heptasaccharide lipid intermediate. More than 30 Congenital Disorders of Glycosylation (CDGs) are associated with this pathway, including RFT1-CDG which results from defects in the membrane protein Rft1. Rft1 is essential for the viability of yeast and mammalian cells and was proposed as the transporter needed to flip the heptasaccharide lipid intermediate across the ER membrane. However, other studies indicated that Rft1 is not required for heptasaccharide lipid flipping in microsomes or unilamellar vesicles reconstituted with ER membrane proteins, nor is it required for the viability of at least one eukaryote. It is therefore not known what essential role Rft1 plays in N -glycosylation. Here, we present a molecular characterization of human Rft1, using yeast cells as a reporter system. We show that it is a multi-spanning membrane protein located in the ER, with its N and C-termini facing the cytoplasm. It is not N -glycosylated. The majority of RFT1-CDG mutations map to highly conserved regions of the protein. We identify key residues that are important for Rft1’s ability to support N -glycosylation and cell viability. Our results provide a necessary platform for future work on this enigmatic protein.

  PublisherOA PDFDOI

• Insertases scramble lipids: Molecular simulations of MTCH2

  Structure · 2024-02-19 · 38 citations

  articleOpen access

  Scramblases play a pivotal role in facilitating bidirectional lipid transport across cell membranes, thereby influencing lipid metabolism, membrane homeostasis, and cellular signaling. MTCH2, a mitochondrial outer membrane protein insertase, has a membrane-spanning hydrophilic groove resembling those that form the lipid transit pathway in known scramblases. Employing both coarse-grained and atomistic molecular dynamics simulations, we show that MTCH2 significantly reduces the free energy barrier for lipid movement along the groove and therefore can indeed function as a scramblase. Notably, the scrambling rate of MTCH2 in silico is similar to that of voltage-dependent anion channel (VDAC), a recently discovered scramblase of the outer mitochondrial membrane, suggesting a potential complementary physiological role for these mitochondrial proteins. Finally, our findings suggest that other insertases which possess a hydrophilic path across the membrane like MTCH2, can also function as scramblases.

  PublisherOA PDFDOI

Recent grants

• Rhodopsin dimerization: mechanistic basis and functional consequences

  NIH · $2.2M · 2017–2022

• NIH Grant R01GM071041

  NIH · $2.8M · 2014

• NIH Grant R01GM055427

  NIH · $3.6M · 2012

• Rhodopsin-mediated phospholipid flipping

  NIH · $462k · 2014–2017

• NIH Grant R01AI028858

  NIH · $1.1M · 1997

Frequent coauthors

• George Cross

  37 shared

• Michael A. J. Ferguson

  Boston Children's Museum

  29 shared

• Satyajit Mayor

  National Centre for Biological Sciences

  24 shared

• George Khelashvili

  Cornell University

  21 shared

• Peter Bütikofer

  University of Bern

  17 shared

• Sumana Sanyal

  University of Oxford

  17 shared

• Kalpana Pandey

  Netaji Subhas University of Technology

  17 shared

• Jolanta Vidugirienė

  Promega (United States)

  16 shared

Labs

• Menon LabPI

Education

• Postdoctoral Associate, Molecular Parasitology

  Rockefeller University

  1989

• Ph.D., Chemistry

  Cornell University

  1986

• M.Sc., Chemistry

  Indian Institute of Technology Kanpur

  1980