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Articles by M. A Hossain
Total Records ( 2 ) for M. A Hossain
  S Ma , F. E Olucha Bordonau , M. A Hossain , F Lin , C Kuei , C Liu , J. D Wade , S. W Sutton , A Nunez and A. L. Gundlach

Hippocampal theta rhythm is thought to underlie learning and memory, and it is well established that "pacemaker" neurons in medial septum (MS) modulate theta activity. Recent studies in the rat demonstrated that brainstem-generated theta rhythm occurs through a multisynaptic pathway via the nucleus incertus (NI), which is the primary source of the neuropeptide relaxin-3 (RLN3). Therefore, this study examined the possible contribution of RLN3 to MS activity, and associated hippocampal theta activity and spatial memory. In anesthetized and conscious rats, we identified the ability of intraseptal RLN3 signaling to modulate neuronal activity in the MS and hippocampus and promote hippocampal theta rhythm. Behavioral studies in a spontaneous alternation task indicated that endogenous RLN3 signaling within MS promoted spatial memory and exploratory activity significantly increased c-Fos immunoreactivity in RLN3-producing NI neurons. Anatomical studies demonstrated axons/terminals from NI/RLN3 neurons make close contact with septal GABAergic (and cholinergic) neurons, including those that project to the hippocampus. In summary, RLN3 neurons of the NI can modulate spatial memory and underlying hippocampal theta activity through axonal projections to pacemaker neurons of the MS. NI/RLN3 neurons are highly responsive to stress and express corticotropin-releasing factor type-1 receptors, suggesting that the effects observed could be an important component of memory processing associated with stress responses.

  M. A Hossain , R Nakano , K Nakamura , M. T Hossain and Y. Kimura

It has been reported that acidic -mannosidase activity increases during tomato fruit ripening, suggesting the turnover of N-glycoproteins is deeply associated with fruit ripening. As part of a study to reveal the relationship between the plant -mannosidase activity and fruit maturation at the molecular level, we have already purified and characterized an -mannosidase from tomato fruit (Hossain et al., Biosci. Biotechnol. Biochem. 2009;73:140–146). In this article, we describe the identification and expression of the tomato acidic -mannosidase gene using the yeast-expression system. The -mannosidase-gene located at chomosome 6 is a 10 kb spanned containing 30 exons. The gene-encoded-protein is single polypeptide chain of 1,028 amino acids containing glycosyl hydrolase domain-38 with predicted molecular mass of 116 kDa. The recombinant enzyme showed maximum activity at pH 5.5, and was almost completely inhibited by both of 1-deoxymannojirimycin and swainsonine. The recombinant -mannosidase, like the native enzyme, could cleave 1-2, 1-3 and 1-6 mannosidic linkage from both high-mannose and truncated complex-type N-glycans. A molecular 3D modelling shows that catalytically important residues of animal lysosomal -mannosidase could be superimposed on those of tomato -mannosidase, suggesting that active site conformation is highly conserved between plant acidic -mannosidase and animal lysosomal -mannosidase.

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