Molecular Basket Research Articles

Crystal structure of glycine N-methyltransferase from rat liver.

Glycine N-methyltransferase (GNMT) from rat liver is a tetrameric enzyme with 292 amino acid residues in each identical subunit and catalyzes the S-adenosylmethionine (AdoMet) dependent methylation of glycine to form sarcosine. The crystal structure of GNMT complexed with AdoMet and acetate, a competitive inhibitor of glycine, has been determined at 2.2 A resolution. The subunit of GNMT forms a spherical shape with an extended N-terminal region which corks the entrance of active site of the adjacent subunit. The active site is located in the near center of the spherical subunit. As a result, the AdoMet and acetate in the active site are completely surrounded by amino acid residues. Careful examination of the structure reveals several characteristics of GNMT. (1) Although the structure of the AdoMet binding domain of the GNMT is very similar to those of other methyltransferases recently determined by X-ray diffraction method, an additional domain found only in GNMT encloses the active site to form a molecular basket, and consequently the structure of GNMT looks quite different from those of other methyltransferases. (2) This unique molecular structure can explain why GNMT can capture folate and polycyclic aromatic hydrocarbons. (3) The unique N-terminal conformation and the subunit structure can explain why GNMT exhibits positive cooperativity in binding AdoMet. From the structural features of GNMT, we propose that the enzyme might be able to capture yet unidentified molecules in the cytosol and thus participates in various biological processes including detoxification of polycyclic aromatic hydrocarbons. In the active site, acetate binds near the S-CH3 moiety of AdoMet. Simple modeling indicates that the amino group of the substrate glycine can be placed close to the methyl group of AdoMet within 3.0 A and form a hydrogen bond with the carboxyl group of Glu15 of the adjacent subunit. On the basis of the ternary complex structure, the mechanism of the methyl transfer in GNMT has been proposed.

X‐ray structure of a molecular basket. Origin of its poor binding properties

AbstractX‐ray analysis and 1H‐NMR data in solution show that the entrance of the cavity of receptor 1c is blocked by benzyl groups, preventing the binding of substrate molecules.

Basket cells in the monkey fascia dentata: A Golgi/electron microscopic study

This study describes non-granule cells in the fascia dentata of rhesus monkeys and baboons. Their cell bodies are located in the molecular layer and at the hilar border of the granular layer. They are called basket cells since their axons give rise to collaterals that branch in the close vicinity of the parent cell body and form symmetric synapses with dendrites and cell bodies of granule cells. These neurons are further classified with regard to the shape and location of their cell bodies and the orientation of their dendrites. Basket cells in the molecular layer are mainly bipolar with dendrites oriented perpendicular to the granular layer. These dendrites are densely innervated by presynaptic boutons forming asymmetric synapses. We have rarely observed molecular layer basket cells with dendrites traversing the granular layer and invading the hilus. We thus conclude that these cells are mainly activated by extrinsic afferents terminating in the molecular layer. Basket cells at the hilar border display pyramidal, fusiform or multipolar cell bodies that give rise to apical dendrites traversing the molecular layer and basal dendrites invading the hilar region. Large boutons establish asymmetric synapses with identified basal dendrites of these neurons. The dendrites of all types of basket cell are smooth, i.e. they had few or no spines. Many of them display varicosities. Cell counts in Cresyl Violet-stained sections revealed a ratio of basket cells to granule cells of 1:500. Essentially, the types of basket cell in the monkey fascia dentata are similar to those described previously for the rat. This contrasts sharply to our recent findings for pyramidal neurons and granule cells of the monkey hippocampus which showed an increased complexity and variability when compared with rodents. These data do not support the hypothesis that only local circuit neurons evolve in phylogeny.

Mit Donorzentren versehener korbförmiger Molekülhohlraum — Darstellung, Struktur, Eigenschaften

Basket‐shaped Molecular Cavity‐Containing Donor Centres — Synthesis, Structure, PropertiesThe macrocyclic basket‐shaped molecule 2, composed of three 4‐donor‐substituted pyridine units, is synthesized by cyclisation of the chloromethyl compound 7 with sulfonamide 8. The X‐ray structure analysis of 2 gives an impression of the shape of the molecular basket. Furthermore it demonstrates that the toluenesulfonamide residues interlink, creating dimeric units of 2 in the crystal.