Biology subjects

Krauss, U.

Publications and source records attributed to Krauss, U..

4 recordsLinked to original sources

bioRxiv2025

Dimer asymmetry in signaling of blue-light sensor histidine kinases

Photoreceptor sensory histidine kinases (SHKs) couple light absorption to conformational changes regulating two-component signaling. Despite their importance and widespread use in optogenetics, the underlying structural signaling mechanisms remain poorly understood. We here engineered dimeric SHKs based on Pseudomonas putida short light-oxygen-voltage (LOV) proteins and determined their crystal structures. Regardless of illumination, the structures adopted a light-state like LOV-LOV dimer with symmetric/straight kinase modules. In contrast, small-angle X-ray scattering together with functional assays revealed pronounced light-dependent rearrangements in solution and allowed the assignment of the kinase-ON dark state to an asymmetric/kinked conformation, whereas the light state adopts a symmetric/straight structure. Comparative analyses of natural and engineered SHKs identified conserved motifs linking LOV domain rotation to kinase activity. The findings highlight the central role of dimer asymmetry and flexibility in SHK signaling, thereby not least informing the engineering of new light-responsive signaling systems.

biochemistry↗

bioRxiv2024

Magnetic Protein Aggregates Generated by Supramolecular Assembly of Ferritin Cages - A Modular Strategy for the Immobilization of Enzymes

Efficient and cost-effective immobilization methods are crucial for advancing the utilization of enzymes in industrial biocatalysis. To this end, in vivo immobilization methods relying on the completely biological production of immobilizates represent an interesting alternative to conventional carrier-based immobilization methods. In this contribution, we present a novel immobilization strategy utilizing in vivo produced, magnetic protein aggregates (MPAs). MPA production is facilitated by the expression of gene fusions consisting of genes encoding for the yellow fluorescent protein variant citrine and variants of the iron storage protein ferritin, including a magnetically enhanced ferritin mutant from Escherichia coli. Expression of the gene fusions allows supramolecular assembly of the fusion proteins in vivo, which is driven by citrine-dependent dimerization of ferritin cages. Upon cell lysis, the assemblies coalesce in solution to form MPAs. The fusion of the mutant E. coli ferritin to citrine yields fluorescent, insoluble protein aggregates that display magnetic properties, verified by their attraction to neodymium magnets. We further demonstrate that these novel, fully in vivo produced protein aggregates can be magnetically purified without the need for ex vivo iron-loading. Utilizing a bait/prey strategy, MPAs were functionalized by the post-translational attachment of an alcohol dehydrogenase to the MPA particles to enable proof-of-concept for enzyme immobilization, giving rise to catalytically-active magnetic protein aggregates (CatMPAs). The resulting (Cat)MPAs could easily be obtained from crude cell extracts via centrifugation, or purified using magnetic columns, and exhibited superior stability. The strategy presented here therefore represents a highly modular method to produce magnetic enzyme immobilizates which can be obtained with high purity.

biochemistry↗

bioRxiv2021

Structural and mechanistic insight into spectral tuning in flavin-binding fluorescent proteins

Determining the molecular origin of spectral tuning in photoactive biological systems is instrumental for understanding their function. Spectral-tuning efforts for flavin-binding fluorescent proteins (FbFPs), an emerging class of fluorescent reporters, are limited by their dependency on protein-bound flavins, whose structure and hence electronic properties, cannot be altered by mutation. To address those shortcomings, we here present the photophysical, computational and structural characterization of structurally uncharacterized blue-shifted FbFPs, carrying a previously described lysine substitution within their flavin-binding pocket. X-ray structures reveal displacement of the lysine away from the chromophore and opening up of the structure as cause for the blue shift. Site-saturation mutagenesis and high-throughput screening, yielded a red-shifted variant, in which the lysine side chain of the blue-shifted variant is stabilized in close distance to the flavin by a secondary mutation, mechanistically accounting for the red shift. Thus, a single secondary mutation in a blue-shifted variant is sufficient to generate a red-shifted FbFP. Using spectroscopy, X-ray crystallography and quantum mechanics molecular mechanics calculations, we provide a firm structural and functional understanding of spectral tuning in FbFPs. We also show that the identified blue- and red-shifted variants allow for two-color microscopy based on spectral separation. In summary, the generated blue- and red-shifted variants represent promising new tools that should find application in life sciences.

biophysics↗

bioRxiv2018

A story of nasal horns: A new species of Iguana Laurenti, 1768 (Squamata, Iguanidae) in Saint Lucia, St Vincent & the Grenadines, and Grenada (Southern Lesser Antilles) and its implications for the taxonomy of the genus Iguana

The Lesser Antilles, in the Eastern Caribbean, were long considered to have only two species in the genus Iguana Laurenti 1768: the Lesser Antillean iguana Iguana delicatissima, which is endemic to parts of the Lesser Antilles, and the common green iguana Iguana iguana, which also occurs throughout Central and South America. However, herpetologists and reptile collectors have pointed out strong physical differences between some of the island populations of Iguana iguana and those from the continent. Drawing on both morphological and genetic data, this paper describes a third species Iguana insularis sp. nov. from the southern Lesser Antilles, specifically the countries of Saint Lucia, St Vincent & the Grenadines, and Grenada. The new species is described based on the following unique combination of characters: Presence of high median and medium to small lateral horns on the snout; Small subtympanic plate not exceeding 20% of the eardrum size; Two or three scales of decreasing size anterior to the subtympanic plate; Fewer than ten small to medium triangular gular spikes; Medium sized dewlap; Low number of small to medium dispersed nuchal tubercles; Dark brown iris, with the white of the eye visible; Oval, prominent nostril; Short and relatively flat head; High dorsal spines; No swelling of the jowls in reproductively active males; Colour of head, body and tail changing from green to pale grey or creamy white in old adults; Vertical black stripes on body and tail, fading with age in some populations. This paper furthermore distinguishes two subspecies: Iguana insularis insularis from the Grenada Bank (comprising Grenada and the Grenadine islands), and Iguana insularis sanctaluciae from Saint Lucia. The form on the island of Saint Vincent has not been identified. Both subspecies are globally threatened by unsustainable hunting (including the pet trade) and by invasive alien species, including hybridization from invasive iguanas from South and Central America (I. iguana and I. rhinolopha, considered here as full species) that have become established in all three countries. The authors call for stronger measures to conserve the remaining purebred Iguana insularis sp. nov. throughout its range and for further research to identify other cryptic species and subspecies of Iguana in the Lesser Antilles.

zoology↗