Vitamin B12 Transport in Bacteria:A structural and biochemical study to identify new transport systems

Uptake of vitamin B12 is essential for many bacteria, but in most cases the membrane proteins involved in transport still need to be identified. Here, the biochemical characterization and high-resolution crystal structure determination of ECF-CbrT and BtuM, two predicted bacterial vitamin B12 uptake systems. ECF-CbrT belongs to the energy coupling factor (ECF-) type ABC-transporter superfamily, which use energy from ATP hydrolysis to power transport. ECF-transporter consist of four components, two that use ATP to fuel transport and one that acts, among other functions, as a scaffold, which together form the tripartite ECF-module. The fourth component acts as a membrane embedded substrate-binding protein. ECF-CbrT exhibits all typical features of an ECF-transporter and binds vitamin B12 with high affinity. Additionally, by measuring transport of vitamin B12 in a defined, reconstituted system allowed for the characterization of the overall transport reaction. The second protein presented here is BtuM, which has no similarity on the sequence level with any other known proteins, but surprisingly is structurally related to the substrate binding component of ECF-type transporters. In contrast to ECF transporters, BtuM does not require the other three components for transport. Therefore, BtuM represents a novel class of ECF-module independent transporters. Additionally, BtuM uses an unprecedented thiolate coordination to bind vitamin B12 that allows for chemical modification. The latter feature is extraordinarily rare among membrane transporters. The results presented in this thesis shed light on the diversity of transporters for vitamin B12 and pave the way for future research and anti-microbial drug design

Cysteine-mediated decyanation of vitamin B12 by the predicted membrane transporter BtuM

Uptake of vitamin B12 is essential for many prokaryotes, but in most cases the membrane proteins involved are yet to be identified. We present the biochemical characterization and high-resolution crystal structure of BtuM, a predicted bacterial vitamin B12 uptake system. BtuM binds vitamin B12 in its base-off conformation, with a cysteine residue as axial ligand of the corrin cobalt ion. Spectroscopic analysis indicates that the unusual thiolate coordination allows for decyanation of vitamin B12. Chemical modification of the substrate is a property other characterized vitamin B12-transport proteins do not exhibit

Intensiv farbige Bor-dotierte Thiazolthiazole durch reduktive Dimerisierung von Borisothiocyanaten

Die Reduktion von (CAAC)BBr2(NCS) (CAAC=cyclisches Alkyl(amino)carben) in der Gegenwart einer Lewis-Base L liefert dreifach koordinierte (CAAC)LB(NCS)-Borylene, die eine reversible (E)/(Z)-Isomerisierung eingehen. Die gleiche Reduktion in Abwesenheit von L führt zu intensiv blauen, bis(CAAC)-stabilisierten, Bor-dotierten, aromatischen Thiazolthiazolen, die aus der Dimerisierung zweifach koordinierter (CAAC)B(NCS)-Borylenintermediate resultieren

Highly colored boron-doped thiazolothiazoles from the reductive dimerization of boron isothiocyanates

Reduction of (CAAC)BBr2(NCS) (CAAC=cyclic alkyl(amino)carbene) in the presence of a Lewis base L yields tricoordinate (CAAC)LB(NCS) borylenes which undergo reversible E/Z‐isomerization. The same reduction in the absence of L yields deep blue, bis(CAAC)‐stabilized, boron‐doped, aromatic thiazolothiazoles resulting from the dimerization of dicoordinate (CAAC)B(NCS) borylene intermediates

The statistical neuroanatomy of frontal networks in the macaque

We were interested in gaining insight into the functional properties of frontal networks based upon their anatomical inputs. We took a neuroinformatics approach, carrying out maximum likelihood hierarchical cluster analysis on 25 frontal cortical areas based upon their anatomical connections, with 68 input areas representing exterosensory, chemosensory, motor, limbic, and other frontal inputs. The analysis revealed a set of statistically robust clusters. We used these clusters to divide the frontal areas into 5 groups, including ventral-lateral, ventral-medial, dorsal-medial, dorsal-lateral, and caudal-orbital groups. Each of these groups was defined by a unique set of inputs. This organization provides insight into the differential roles of each group of areas and suggests a gradient by which orbital and ventral-medial areas may be responsible for decision-making processes based on emotion and primary reinforcers, and lateral frontal areas are more involved in integrating affective and rational information into a common framework