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A carboxy-terminal fragment of colicin Ia forms ion channels (1993)

Ghosh, Partho ; Mel, Stephanie F. ; Stroud, Robert M.

Springer

The journal of membrane biology 134 (1993), S. 85-92

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ISSN: 1432-1424

Keywords: Colicin Ia fragment ; Artificial lipid bilayers ; Ion channels ; Proteolysis

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Abstract A carboxy-terminal, 18 kD fragment of colicin Ia, a bacterial toxin, forms ion channels in artificial phospholipid bilayers. This fragment, which comprises a quarter of the intact 70 kD molecule, is resistant to extensive protease digestion and probably constitutes a structural domain of the protein. The ion channels formed by the 18 kD fragment are functionally heterogeneous, having conductances that range from 15 to 30 pS at positive voltages and from 70 to 250 pS at negative voltages, and open lifetimes that range from at least 25 msec to 5 sec. In contrast, ion channels formed by whole colicin Ia open only at negative voltages, at which their conductances range from 6 to 30 pS, and their open lifetimes range from 1 sec to 3 min. Additionally, the open state of the 18 kD fragment channel is characterized by noisy fluctuations in current, while the open state of the whole molecule ion channel is often marked by numerous, stable subconductance states. Since the properties of the fragment channel differ substantially from those of the whole molecule channel, we suggest that portions of the molecule outside of the 18 kD fragment are involved in forming the whole molecule ion channel.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00232745

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Plastic adaptation toward mutations in proteins: Structural comparison of thymidylate synthases (1990)

Perry, Kathy M. ; Fauman, Eric B. ; Finer-Moore, Janet S. ; [et al.]

New York, NY : Wiley-Blackwell

Proteins: Structure, Function, and Genetics 8 (1990), S. 315-333

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ISSN: 0887-3585

Keywords: thymidylate synthase ; plasticity ; crystal structure ; B factor ; mutation ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The structure of thymidylate synthase (TS) from Escherichia coli was solved from cubic crystals with a = 133 Å grown under reducing conditions at pH 7.0, and refined to R = 22% at 2.1 Å resolution. The structure is compared with that from Lactobacillus casei solved to R = 21% at 2.3 Å resolution. The structures are compared using a difference distance matrix, which identifies a common core of residues that retains the same relationship to one another in both species. After subtraction of the effects of a 50 amino acid insert present in Lactobacillus casei, differences in position of atoms correlate with temperature factors and with distance from the nearest substituted residue. The dependence of structural difference on thermal factor is parameterized and reflects both errors in coordinates that correlate with thermal factor, and the increased width of the energy well in which atoms of high thermal factor lie. The dependence of structural difference on distance from the nearest substitution also depends on thermal factors and shows an exponential dependence with half maximal effect at 3.0 Å from the substitution. This represents the plastic accommodation of the protein which is parameterized in terms of thermal B factor and distance from a mutational change.

Additional Material: 16 Ill.