Computational modelling of amino acid exchange and facilitated transport in placental membrane vesicles.
Computational modelling of amino acid exchange and facilitated transport in placental membrane vesicles.
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DOI：
10.1016/j.jtbi.2014.10.042
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发表时间：
2015-01-21
影响因子：
2
通讯作者：
Sengers, B. G.
中科院分区：
文献类型：
--
作者：
Panitchob, N.;Widdows, K. L.;Crocker, I. P.;Hanson, M. A.;Johnstone, E. D.;Please, C. P.;Sibley, C. P.;Glazier, J. D.;Lewis, R. M.;Sengers, B. G.
胎盘氨基酸转运是胎儿发育所必需的，而胎盘氨基酸转运受损与胎儿发育不良有关。众所周知，胎盘氨基酸的转运是由一系列具有重叠底物特异性的特异膜转运蛋白介导的。然而，这些转运体是如何单独或作为一个综合系统发挥作用的，目前还不完全清楚。我们认为，数学模型可以帮助进一步阐明这些转运蛋白如何调节胎盘氨基酸运输的潜在机制。这项工作的目的是对丝氨酸的钠独立转运进行建模，丝氨酸的转运被认为遵循强制性交换机制。然而，以前的人胎盘微绒毛质膜囊泡的氨基酸摄取实验一直产生似乎与这种机制不相容的结果；即，在零反式条件下观察到了转运，囊泡内没有内部底物来驱动交换。这一观察提出了两种可供选择的假说：(I)交换不是完全强制性的，或者(Ii)交换确实是强制性的，但囊泡内存在不可预见的氨基酸底物浓度，这可能会驱动交换。为了研究这些可能性，基于载体介导的传输建立了示踪剂吸收的数学模型，该模型可以表示促进扩散或强制性交换(也分别称为单端口和反端口机制)。体外测定了胎盘微绒毛膜囊泡对丝氨酸的摄取，并根据测得的表观Michaelis-Menten参数Km和Vmax对模型进行了解释。此外，在模型预测的基础上，进行了一个新的时间序列实验来区分假设的转运蛋白机制。对结果的分析表明，囊泡中存在促进转运的成分，而基于该模型，没有发现内源氨基酸在囊泡中大量存在的证据。胎盘膜泡摄取丝氨酸的初始速率和时间进程数据。促进扩散与强制性交换的综合模型分析。表观米氏常数与体内浓度的相关性。胎盘囊泡的摄取与促进性转运成分一致。任何内源性底物对囊泡均无明显影响。
Placental amino acid transport is required for fetal development and impaired transport has been associated with poor fetal growth. It is well known that placental amino acid transport is mediated by a broad array of specific membrane transporters with overlapping substrate specificity. However, it is not fully understood how these transporters function, both individually and as an integrated system. We propose that mathematical modelling could help in further elucidating the underlying mechanisms of how these transporters mediate placental amino acid transport. The aim of this work is to model the sodium independent transport of serine, which has been assumed to follow an obligatory exchange mechanism. However, previous amino acid uptake experiments in human placental microvillous plasma membrane vesicles have persistently produced results that are seemingly incompatible with such a mechanism; i.e. transport has been observed under zero-trans conditions, in the absence of internal substrates inside the vesicles to drive exchange. This observation raises two alternative hypotheses; (i) either exchange is not fully obligatory, or (ii) exchange is indeed obligatory, but an unforeseen initial concentration of amino acid substrate is present within the vesicle which could drive exchange. To investigate these possibilities, a mathematical model for tracer uptake was developed based on carrier mediated transport, which can represent either facilitated diffusion or obligatory exchange (also referred to as uniport and antiport mechanisms, respectively). In vitro measurements of serine uptake by placental microvillous membrane vesicles were carried out and the model applied to interpret the results based on the measured apparent Michaelis–Menten parameters Km and Vmax. In addition, based on model predictions, a new time series experiment was implemented to distinguish the hypothesised transporter mechanisms. Analysis of the results indicated the presence of a facilitated transport component, while based on the model no evidence for substantial levels of endogenous amino acids within the vesicle was found. Initial rate and time course data for serine uptake in placental membrane vesicles. Integrated model analysisof facilitative diffusion vs obligatory exchange. Dependency apparent Michaelis–Menten constants on internal concentrations. Uptake in placental vesicles was consistent with a facilitative transport component. No effects of any internal endogenous substrate in vesicles were apparent.
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影响因子：
4.1
作者：
GANAPATHY, ME;LEIBACH, FH;GANAPATHY, V
通讯作者：
GANAPATHY, V
影响因子：
6.8
作者：
Khalili-Araghi, Fatemeh;Gumbart, James;Wen, Po-Chao;Sotomayor, Marcos;Tajkhorshid, Emad;Schulten, Klaus
通讯作者：
Schulten, Klaus
影响因子：
2
作者：
Gill, J. S.;Salafia, C. M.;Vvedensky, D. D.
通讯作者：
Vvedensky, D. D.
影响因子：
3.4
作者：
BLUMENTHAL, R;KEDEM, O
通讯作者：
KEDEM, O
影响因子：
3.8
作者：
Lewis, R. M.;Glazier, J.;Hanson, M. A.
通讯作者：
Hanson, M. A.