Agricultural Implements of the Roman World. By K. D. W<scp>hite</scp>

Bowen, H. C.

doi:10.1080/00665983.1968.11078357

Cited by 3 publications

(3 citation statements)

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“…Breast, colon, and skin cancer cells have an unusual distribution of cell-surface complex oligosaccharides, with increased GlcNAc branching on the trimannosyl core , correlated with disease progression. , Inhibition of Golgi α-mannosidase (GMII) with swainsonine blocks the abnormal formation of complex oligosaccharides, leading to reduced metastasis and tumor growth. , However, swainsonine also inhibits the closely related lysosomal α-mannosidase, limiting its clinical use. ,, …”

Section: Introductionmentioning

confidence: 99%

Molecular Mechanism of the Glycosylation Step Catalyzed by Golgi α-Mannosidase II: A QM/MM Metadynamics Investigation

et al. 2010

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Golgi alpha-mannosidase II (GMII), a member of glycoside hydrolase family 38, cleaves two mannosyl residues from GlcNAcMan(5)GlcNAc(2) as part of the N-linked glycosylation pathway. To elucidate the molecular and electronic details of the reaction mechanism, in particular the conformation of the substrate at the transition state, we performed quantum mechanics/molecular mechanics metadynamics simulations of the glycosylation reaction catalyzed by GMII. The calculated free energy of activation for mannosyl glycosylation (23 kcal/mol) agrees very well with experiments, as does the conformation of the glycon mannosyl ring in the product of the glycosylation reaction (the covalent intermediate). In addition, we provide insight into the electronic aspects of the molecular mechanism that were not previously available. We show that the substrate adopts an (O)S(2)/B(2,5) conformation in the GMII Michaelis complex and that the nucleophilic attack occurs before complete departure of the leaving group, consistent with a D(N)A(N) reaction mechanism. The transition state has a clear oxacarbenium ion (OCI) character, with the glycosylation reaction following an (O)S(2)/B(2,5) --> B(2,5) [TS] --> (1)S(5) itinerary, agreeing with an earlier proposal based on comparing alpha- and beta-mannanases. The simulations also demonstrate that an active-site Zn ion helps to lengthen the O2'-H(O2') bond when the substrate acquires OCI character, relieving the electron deficiency of the OCI-like species. Our results can be used to explain the potency of recently formulated GMII anticancer inhibitors, and they are potentially relevant in deriving new inhibitors.

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Section: Introductionmentioning

confidence: 99%

Molecular Mechanism of the Glycosylation Step Catalyzed by Golgi α-Mannosidase II: A QM/MM Metadynamics Investigation

et al. 2010

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“…The alkaloids swainsonine and mannostatin are potent inhibitors of Golgi α-mannosidase II . However, these compounds also inhibit the GH38 lysosomal α-mannosidases (LM) with potencies equal to those of the GMII and therefore induce symptoms similar to those of the lysosomal storage disease α-mannosidosis. ,– Attempts to develop more selective inhibitors of GMII by chemically modifying swainsonine or mannostatin have been unsuccessful to date. – ,, Understanding the molecular basis for the substrate specificities of these enzymes may provide unique opportunities for the design of more selective inhibitors.…”

Section: Introductionmentioning

confidence: 99%

Probing the Substrate Specificity of Golgi α-Mannosidase II by Use of Synthetic Oligosaccharides and a Catalytic Nucleophile Mutant

et al. 2008

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Inhibition of Golgi α-mannosidase II (GMII), which acts late in the N-glycan processing pathway, provides a route to blocking cancer-induced changes in cell surface oligosaccharide structures. To probe the substrate requirements of GMII, oligosaccharides were synthesized that contained an α(1,3)-or α(1,6)-linked 1-thiomannoside. Surprisingly, these oligosaccharides were not observed in X-ray crystal structures of native Drosophila GMII (dGMII). However, a mutant enzyme in which the catalytic nucleophilic aspartate was changed to alanine (D204A) allowed visualization of soaked oligosaccharides and led to the identification of the binding site for the α(1,3)-linked mannoside of the natural substrate. These studies also indicate that the conformational change of the bound mannoside to a high-energy B 2,5 conformation is facilitated by steric hindrance from, and the formation of strong hydrogen bonds to, Asp204. The observation that 1-thio-linked mannosides are not well tolerated by the catalytic site of dGMII led to the synthesis of a pentasaccharide containing the α(1,6)-linked Man of the natural substrate and the β(1,2)-linked GlcNAc moiety proposed to be accommodated by the extended binding site of the enzyme. A cocrystal structure of this compound with the D204A enzyme revealed the molecular interactions with the β(1,2)-linked GlcNAc. The structure is consistent with the ~80-fold preference of dGMII for the cleavage of substrates containing a nonreducing β(1,2)-linked GlcNAc. By contrast, the lysosomal mannosidase lacks an equivalent GlcNAc binding site and kinetic analysis indicates oligomannoside substrates without non-reducing-terminal GlcNAc modifications are preferred, suggesting that selective inhibitors for GMII could exploit the additional binding specificity of the GlcNAc binding site.

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“…8 Figure 3 shows the experimental I 0 Ϫ I vs R plot. 10 The authors thank Dr. M. Ito of Himeji Inst. The data below 10000 cps seem to systematically deviate from a straight line, which is especially conspicuous for the modified amplifier.…”

Section: Masaaki Harada and Kenji Sakuraimentioning

confidence: 98%