发信人: doggiebear (doggiebear), 信区: Biology
标 题: SBIG: Channels - 6
发信站: Unknown Space - 未名空间 (Fri Oct 17 00:29:37 2003) WWW-POST


how the channel select the ion? Charge and dimension. yes.
So how about potssium channel?

Look at this figure again.




http://www.hhmi.org/research/investigators/images/mackinnon_fig1_lg.gif


the second pannel of the right figure. The backbone partial negatively charged
carbonyl oxygen atoms actually interact with the postively charged potassium.
Also the partical negative charge from C-term of helices play crucial part.

this is also true for chloride channel, though the geometry of its selective
filter is different. Chloride channel uses the partial positve charges from
the Ser and Tyr side chain hydroxyl groups, as well as the positively partial
charged N-term of helices.

Why only use partial charges? why not use fully charged residues, like Arg lys
or Glu? Answer, they are too strong. The function of the selective filter is
to have some binding to select the right ion and also stabilize the ion but
not bind the ion too tightly to prevent its transportation. Partial charges
solve both problems.

The lesson:

In biological systme, something weak may be a merit.

Same for weak forces, that contribute largely to protein folding.



--
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Liberalism is something to be proud of!
※ 修改:·doggiebear 於 Oct 17 00:29:37 修改本文·[FROM: 208.180.]
※ 来源:．Unknown Space - 未名空间 mitbbs.com．[FROM: 208.180.]