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Studies of the hyaluronan (HA) tetrasaccharides are important for
understanding hydrogen-bonding in the HA polymer, as they are probably the
smallest oligomers in which characteristics of the constituent
monosaccharides and the polymer are simultaneously exhibited. Here we
present extensive molecular dynamics simulations of the two
tetrasaccharides of HA in dilute aqueous solution. These simulations have
confirmed the existence of intramolecular hydrogen-bonds between the
neighboring sugar residues of HA in solution, as proposed by Scott (1989).
However, our simulations predict that these intramolecular hydrogen-bonds
are not static as previously proposed, but are in constant dynamic exchange
on the sub-nanosecond time-scale. This process results in discrete internal
motion of the HA tetrasaccharides where they rapidly move between low
energy conformations. Specific interactions between water and
intramolecular hydrogen-bonds involving the hydroxymethyl group were found
to result in differing conformations and dynamics for the two alternative
tetrasaccharides of HA. This new observation suggests that this residue may
play a key role in the entropy and stability of HA in solution, allowing it
to stay soluble up to high concentration. The vicinal coupling constants3 J
NHCH of the acetamido groups have been calculated from our aqueous
simulations of HA. We found that high values of 3J NHCH approximately 8 Hz,
as experimentally measured for HA, are consistent with mixtures of both
trans and cis conformations, and thus3 J NHCH cannot be used to imply a
purely trans conformation of the acetamido. The rapid exchange of
intramolecular hydrogen-bonds indicates that although the structure is at
any moment stabilized by these hydrogen-bonds, no one hydrogen-bond exists
for an extended period of time. This could explain why NMR often fails to
provide evidence for intramolecular hydrogen-bonds in HA and other aqueous
carbohydrate structures.
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Carlson A Berkowitz JM Browning D Slamon DJ Gasson JC Yates KE 《DNA and cell biology》2005,24(5):311-316
The cellular fes gene encodes a 93-kilodalton protein-tyrosine kinase (p93) that is expressed in both normal and neoplastic myeloid cells. Increased c-Fes expression is associated with differentiation in normal myeloid cells and cell lines. Our hypothesis was that primary leukemia cells would show a similar pattern of increased expression in more differentiated cells. Therefore, we compared c-Fes expression in cells with an undifferentiated, blast phenotype (acute myelogenous leukemia--AML) to cells with a differentiated phenotype (chronic myelogenous leukemia--CML). Instead of differences in p93 expression levels, we found complex patterns of c-Fes immunoreactive proteins that corresponded with differentiation in normal and leukemic myeloid cells. The "blast" pattern consisted of c-Fes immunoreactive proteins p93, p74, and p70; the "differentiated" pattern showed two additional c-Fes immunoreactive proteins, p67 and p62. Using mRNA from mouse and human cell lines, we found deletion of one or more exons in the c-fes mRNA. Those deletions predicted truncation of conserved domains (CDC15/FCH and SH2) involved in protein-protein interactions. No deletions were found, however, within the kinase domain. We infer that alternative splicing generates a family of c-Fes proteins. This may be a mechanism to direct the c-Fes kinase domain to different subcellular locations and/or substrates at specific stages of myeloid cell differentiation. 相似文献
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