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Title
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Poly-Ig tandems from I-band titin share extended domain arrangements irrespective of the distinct features of their modular constituents.
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Authors
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M.Marino,
D.I.Svergun,
L.Kreplak,
P.V.Konarev,
B.Maco,
D.Labeit,
O.Mayans.
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Ref.
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J Muscle Res Cell Motil, 2005,
26,
355-365.
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PubMed id
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Abstract
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The cellular function of the giant protein titin in striated muscle is a major
focus of scientific attention. Particularly, its role in passive mechanics has
been extensively investigated. In strong contrast, the structural details of
this filament are very poorly understood. To date, only a handful of atomic
models from single domain components have become available and data on
poly-constructs are limited to scarce SAXS analyses. In this study, we examine
the molecular parameters of poly-Ig tandems from I-band titin relevant to muscle
elasticity. We revisit conservation patterns in domain and linker sequences of
I-band modules and interpret these in the light of available atomic structures
of Ig domains from muscle proteins. The emphasis is placed on features expected
to affect inter-domain arrangements. We examine the overall conformation of a
6Ig fragment, I65-I70, from the skeletal I-band of soleus titin using SAXS and
electron microscopy approaches. The possible effect of highly conserved
glutamate groups at the linkers as well as the ionic strength of the medium on
the overall molecular parameters of this sample is investigated. Our findings
indicate that poly-Ig tandems from I-band titin tend to adopt extended
arrangements with low or moderate intrinsic flexibility, independently of the
specific features of linkers or component Ig domains across constitutively- and
differentially-expressed tandems. Linkers do not appear to operate as free
hinges so that lateral association of Ig domains must occur infrequently in
samples in solution, even that inter-domain sequences of 4-5 residues length
would well accommodate such geometry. It can be expected that this principle is
generally applicable to all Ig-tandems from I-band titin.
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