发信人: Marble (小石头哥哥), 信区: Biology
标 题: Re: MCBC 2nd paper (discussion/comment)
发信站: The unknown SPACE (Thu Feb 6 23:34:52 2003), 转信

structural biology is pretty tough, particularly to get crystal for X-ray
analysis of static conformation. otherwise, NMR is used to analyze
conformation(s) in solution. this is my basic understanding of this
issue. this paper has addressed the crystal structure of mechano-
sensitive channel of small conductance (MscS ) at 3.9 angstroms
resolution (not very high). compared with MscL that has large
conductance, the MscS is also mechanosensitive, yet the opening
pressure is lower. MscS has more extensive distributions than MscL
and membrane depoolarization also contributes to channel opening.
as structure for voltage-gated channel is not available till today,
this structural model for MscS provides some useful clue to predict
the mechanism of channel opening.

to get idea about structure of a biomolecule, it is important to
determine the three-dimentional arrangement of the constituents.
electron desity map was constructed from e. coli MscS crystal,
while selenomethionine was used to substitute methionine and
later used as marker for positioning. in general, 7 MscS polypeptides
form a pore on the membrane. you can imagine the basic 3D image
as a carrier made of bamboo sheet.
( )
( )
so it responds to tension and thus opens the hole . however, the
peptides definitely cannot be stretched that much. a couple of
implications about the structure, as discussed in the manuscript,
include modeling mechanosensitive channel with small amino acid
such as Ala and Gly, involvement of positively charged amino acid
such as Arg in voltage gating, as well as the extramembrane domain
forming potential selective filter for permeation, etc.

this is my understanding, and typically i do not ask question during a
seminar devoted to structural biologists. if i do, i only ask where are
the point mutations located on the structural motif.










: Science 2002 November 22; 298: 1582-1587.
: 2. Questions:
: 1) According to this paper, what is the difference
: between MscS and MscL.
: 2) What tech did they use in this paper to reveal


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※ 修改:．Marble 于 Feb 7 00:03:36 修改本文．[FROM: 130.203.]
※ 来源:．The unknown SPACE bbs.mit.edu．[FROM: 130.203.]