Page 168 - The Miracle in the Cell Membrane

N a tu re The 17 January, 2002 edi tion of Nature mag -

a zine car ried three-dimen sion al ima ges of the chlo -
ride ion chan nel, obtained by using X-ray crys tal -
log ra phy. Roderick MacKinnon, a Howard Hughes Institute
research er at Rockefeller University, and his team revealed the
pro tein archi tec ture spe cial ly created for chlo ride ions to pass
through the cell mem brane in the most effi cient man ner. 1
About the com plex struc ture they encoun tered, MacKinnon
said:
It is a com pli cat ed struc ture. "Scientists did an excel lent
job deduc ing many aspects of the chlo ride ion chan nel . . .
To under stand the phys i cal prin ci ples of anion select iv i ty,
an atom ic struc ture is need ed. Although the struc ture is
com pli cat ed, it con veys a sim ple mes sage of how nature
arranged the pro tein to sta bil ize an anion such as chlo ride
inside the mem brane. 2
Living things use elec tri cal ly charged ions for com mu ni ca -
tions of var i ous kinds—con trol of the heart rhythm, the for ma -
tion of nerve sig nals and the secre tion of hor mones. As
explained ear li er, cells use ions to trans mit sig nals by set ting
up an elec tri cal dif fer en tial between the inside and the out side
of the cell. When ions are charged, they pre fer to be in water

At the side you can see how
the chloride channel structure
is organized and the way in
which salt is absorbed into
your cells. Two equal sub-
units, colored blue and green,
are seen in the channel. Each
sub-unit constitutes its own
ion space. The red spheres
show the pathways of chloride
ions.

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