Biology subjects

Zijlstra, N.

Publications and source records attributed to Zijlstra, N..

6 recordsLinked to original sources

bioRxiv2024

Conserved Lysine in transmembrane helix 5 is key for the inner gating of the LAT transporter BasC

L-amino acid transporters (LATs) play a key role in a wide range of physiological processes. Defects in LATs can lead to neurological disorders and aminoacidurias, while the overexpression of these transporters is related to cancer. BasC is a bacterial LAT transporter with an APC fold. In this study, to monitor the cytoplasmic motion of BasC, we developed a smFRET assay that can characterize the conformational states of the intracellular gate in solution at room temperature. Based on combined biochemical and biophysical data and molecular dynamics simulations, we propose a model in which the conserved lysine residue in TM5 supports TM1a to explore both open and closed states within the cytoplasmic gate under apo conditions. This equilibrium can be altered by substrates, mutation of conserved lysine 154 in TM5, or transport-blocking nanobodies. Overall, these findings provide insights into the transport mechanism of BasC and highlight the significance of the lysine residue in TM5 in the cytoplasmic gating of LATs.

biochemistry↗

bioRxiv2023

Single-molecule detection and super-resolution imaging with a portable and adaptable 3D-printed microscopy platform (Brick-MIC)

Over the past decades, single-molecule and super-resolution microscopy have advanced and represent essential tools for life science research. There is,however, a growing gap between the state-of-the-art and what is accessible to biologists, biochemists, medical researchers or labs with financial constraints. To bridge this gap, we introduce Brick-MIC, a versatile and affordable open-source 3D-printed micro-spectroscopy and imaging platform. Brick-MIC enables the integration of various fluorescence imaging techniques with single-molecule resolution within a single platform and exchange between different modalities within minutes. We here present variants of Brick-MIC that facilitate single-molecule fluorescence detection, fluorescence correlation spectroscopy and super-resolution imaging (STORM and PAINT). Detailed descriptions of the hardware and software components, as well as data analysis routines are provided, to allow non-optics specialist to operate their own Brick-MIC with minimal effort and investments. We foresee that our affordable, flexible, and open-source Brick-MIC platform will be a valuable tool for many laboratories worldwide.

biophysics↗

bioRxiv2023

Dissecting Mechanisms of Ligand Binding and Conformational Changes in the Glutamine-Binding Protein

The glutamin-binding protein GlnBP is part of an ATP-binding cassette transporter system in E. coli and uses two well-characterized conformational states, an open ligand-free and a closed-liganded state, to facilitate active amino-acid uptake. Existing literature on its ligand binding mechanism lacked sufficient evidence to univocally assign the kinetic type of binding mechanism for GlnBP: ligand binding prior to conformational change, i.e., an induced fit or the conformational selection, in which the ligand binds the matching conformation from a pre-existing ensemble. Since such mechanistic questions are relevant for our fundamental understanding of how this and other biomacromolecules regulate cellular processes, we here revisit the question for GlnBP. We present a biochemical and biophysical analysis using a combination of calorimetry, single-molecule and surface-plasmon resonance spectroscopy and molecular dynamics simulations. We found that both apo- and holo-GlnBP show no detectable exchange between open and (semi-)closed conformations on timescales between 100 ns and 10 ms and that ligand binding and conformational changes in GlnBP are correlated. A global analysis of our experimental results suggests that the conformational selection model is only compatible with GlnBP for the extreme scenario of very fast conformational exchange between the open and closed states on timescales <100 ns. In contrast all data remains compatible with an induced-fit mechanism, where the ligand binds GlnBP prior to conformational rearrangements. Importantly, our work demonstrates that it is an intricate task to identify the type of kinetic binding mechanism and that this requires not only a sufficient set of data, but also an integrative experimental and theoretical framework to address the question. Based on this concept, we propose that various protein systems, for which so far only insufficient kinetic data are available, should be revisited.

biophysics↗

bioRxiv2022

Enabling spectrally resolved single-molecule localization microscopy at high emitter densities

Single-molecule localization microscopy (SMLM) is a powerful technique for elucidating structure and dynamics in the life- and material sciences with sub-50 nm spatial resolution. The simultaneous acquisition of spectral information (spectrally resolved SMLM, sSMLM) enables multiplexing using spectrally distinct fluorophores or enable the probing of local chemical environments by using solvachromatic fluorophores such as Nile Red. Until now, the widespread utilisation of sSMLM was hampered by several challenges: an increased complexity of the optical detection pathway, limited software solutions for data analysis, lower accessible emitter densities or smaller field-of-views, and overall compromised spatio-spectral resolution. Here, we present a low-cost implementation of sSMLM that addresses these challenges. Using a blazed, low-dispersion transmission grating positioned close to the image plane here represented by the camera sensor, the +1st diffraction order is minimally elongated compared to the point spread function of the 0th order and can therefore be analysed using common subpixel single-molecule localization algorithms. The distance between both PSFs provides accurate information on the spectral properties of the emitter. The minimal excess width of 1st order PSFs enables a fivefold higher emitter density compared to other sSMLM approaches whilst achieving a spatio-spectral localization accuracy sufficient to discriminate between fluorophores whose peak emission are less than 15 nm apart as demonstrated using dSTORM, DNA-PAINT and smFRET. We provide an ImageJ/Fiji plugin (sSMLMAnalyzer) and suitable Matlab scripts for data analysis. We envision that our approach will find widespread use in super-resolution applications that rely on distinguishing spectrally different fluorophores under low photon conditions.

biophysics↗

bioRxiv2020

Structural and biophysical characterization of the tandem substrate-binding domains of the ABC importer GlnPQ

The ATP-binding cassette transporter GlnPQ is an essential uptake system that transports glutamine, glutamic acid, and asparagine in Gram-positive bacteria. It features two extracytoplasmic substrate-binding domains (SBDs) that are linked in tandem to the transmembrane domain of the transporter. The two SBDs differ in their ligand specificities, binding affinities and their distance to the transmembrane domain. Here, we elucidate the effects of the tandem arrangement of the domains on the biochemical, biophysical and structural properties of the protein. For this, we determined the crystal structure of the ligand-free tandem SBD1-2 protein from L. lactis in the absence of the transporter and compared the tandem to the isolated SBDs. We also used isothermal titration calorimetry to determine the ligand-binding affinity of the SBDs and single-molecule Forster-resonance energy transfer (smFRET) to relate ligand binding to conformational changes in each of the domains of the tandem. We show that substrate binding and conformational changes are not notably affected by the presence of the adjoining domain in the wild-type protein, and changes only occur when the linker between the domains is shortened. In a proof-of-concept experiment, we combine smFRET with protein-induced fluorescence enhancement and show that a decrease in SBD linker length is observed as a linear increase in donor-brightness for SBD2 while we can still monitor the conformational states (open/closed) of SBD1. These results demonstrate the feasibility of PIFE-FRET to monitor protein-protein interactions and conformational states simultaneously. HIGHLIGHTSO_LIResolved crystal structure of tandem SBD1-2 of GlnPQ from Lactococcus lactis C_LIO_LIConformational states and ligand binding affinities of individual domains SBD1 and SBD2 are similar to tandem SBD1-2 C_LIO_LINo cooperative effects are seen for different ligands for SBDs in the tandem C_LIO_LIProof of concept experiments show that PIFE-FRET can monitor SBD conformations and protein-protein interaction simultaneously C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/423572v1_ufig1.gif" ALT="Figure 1"> View larger version (87K): org.highwire.dtl.DTLVardef@1fa36f7org.highwire.dtl.DTLVardef@2e973forg.highwire.dtl.DTLVardef@cbae51org.highwire.dtl.DTLVardef@2185cc_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2020

Evolution of structural dynamics in bilobed proteins

Novel biophysical tools allow the structural dynamics of proteins, and the regulation of such dynamics by binding partners, to be explored in unprecedented detail. Although this has provided critical insights into protein function, the means by which structural dynamics direct protein evolution remains poorly understood. Here, we investigated how proteins with a bilobed structure, composed of two related domains from the type-II periplasmic binding protein domain family, have undergone divergent evolution leading to modification of their structural dynamics and function. We performed a structural analysis of ~600 bilobed proteins with a common primordial structural core, which we complemented with biophysical studies to explore the structural dynamics of selected examples by single-molecule Forster resonance energy transfer and Hydrogen-Deuterium exchange mass spectrometry. We show that evolutionary modifications of the structural core, largely at its termini, enables distinct structural dynamics, allowing the diversification of these proteins into transcription factors, enzymes, and extra-cytoplasmic transport-related proteins. Structural embellishments of the core created new interdomain interactions that stabilized structural states, reshaping the active site geometry, and ultimately, altered substrate specificity. Our findings reveal an as yet unrecognized mechanism for the emergence of functional promiscuity during long periods of protein evolution and are applicable to a large number of domain architectures.

biophysics↗