Metabolite uptake across cellular membranes

Diseases such as cardiovascular disease, diabetes and cancer have a dramatic impact on modern society, and in great part are related to uptake of metabolites such as cholesterol and sugar. We still know surprisingly little about the molecular details of the processes that goes on during the uptake of many basic metabolites, and an improved understanding of metabolite uptake has tremendous potential for improving general public health.

We specialize in structure and function of membrane proteins, with a special focus on the transport mechanisms mediating uptake of lipids, vitamins, sugars and ions. We address these topics using a complementary set of methods founded in macromolecular crystallography and electron microscopy to determine the 3-dimensional atomic structures of key players in these transport systems. This is combined with biochemical characterization of the molecular mechanism in vitro and in vivo. We are furthermore engaged in development of methods for low-resolution crystallography and single-particle cryo-electron microscopy, as it pertains to the challenging field of membrane protein structure.

Kidmose et al. Namdinator

Sterol Uptake and Homeostasis

Sterols are an essential component of membranes in all eukaryotic cells and are also the precursor of multiple indispensable cellular metabolites (e.g. estrogen and testosterone in humans).
Universally, the first sterol uptake step in eukaryotes is the endocytosis of lipid particles into degradative organelles called lysosomes. Sterols are integrated into the lysosomal membrane by the Niemann-Pick type C (NPC) system and then reshuffled to other cellular membranes by vesicular and non-vesicular processes using e.g. cytosolic Lipid Transfer Proteins.
Sterol uptake and homeostasis is of high medical relevance for a number of reasons; atherosclerotic cardiovascular disease is linked to cholesterol levels in blood and Filovirus entry (eg. Ebola) into the cell is dependent on this elusive process. The NPC proteins are a highly valuable group of targets to address a range of important human maladies, as well as to improve fundamental understanding of essential sterol uptake pathways for which the molecular mechanism remains almost completely unknown.
Very little is known about the molecular interactions of NPC proteins with substrates and interaction partners, including whether NPC membrane proteins mediate any kind of active transport of sterols. These questions lies at the core of understanding how sterol uptake and homeostasis is maintained and how NPC proteins confer their essential biological function in vivo. The long-term objective of the lab is to elucidate the molecular mechanisms underlying NPC-dependent sterol transport through a combination of crystallography and electron microscopy.

Winkler et al. NPC system in yeast

Sugar Uptake

Sugars are the major cellular source of energy and carbon, and facilitated sugar transport in plants and humans is made possible by sugar transporters belonging to the ubiquitous Sugar Porter (SP) protein family.
In humans, GLUTs, from the SP family, are absolutely essential for basic energy levels in the cell, but are also of particular interest due to their relevance to various diseases, most prominently diabetes, obesity and cancer.
In plants, Sugar Transport Proteins, also from the SP family, are key determinants of monosaccharide uptake into apoplastically isolated organs. STPs control organ development, including the growth and deveopments of seeds (cereals), fruit and roots. The long-term objective of the lab is to understand the molecular mechanism and regulation of transport of sugar in the Sugar Porter family by determining structures, and use this information to guide our biochemical studies of mechanism.

Paulsen et al. Plant Sugar Transporter STP10

Potassium Transport

This project is a collaborative effort together with the group of Prof. David Stokes from New York University.
The KdpFABC complex is a transmembrane protein complex found in prokaryotes with four subunits (KdpA, KdpB, KdpC, KdpF). Of these subunits, KdpA and KdpB form the core, and both are needed for the function of the complex, namely the active transport of potassium against its electrochemical gradient. This transport is powered by the use of cellular ATP. The complex is unique, as it is the only known example of a complex where both a channel-family protein (KdpA) and a pump-family protein (KdpB) work together to create transmembrane ion transport.
To appreciate why this is interesting, recall that the distinction between ion channels and ion pumps is fundamental to membrane biology. Channels are passive conduits where ions rapidly rush down electrochemical gradients. Meanwhile, pumps release energy from e.g. ATP to actively push ions against, and thereby build up, those gradients.
The long-term objective is to elucidate the molecular mechanism of KdpFABC potassium uptake.

Huang et al. KdpFABC complex