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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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Solvent structure in crystals of trypsin determined by X-ray and neutron diffraction (1992)

Finer-Moore, Janet S. ; Kossiakoff, Anthony A. ; Hurley, James H. ; [et al.]

New York, NY : Wiley-Blackwell

Proteins: Structure, Function, and Genetics 12 (1992), S. 203-222

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ISSN: 0887-3585

Keywords: protein folding ; protein structure ; hydrogen bond ; serine protease ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The solvent structure in orthorhombic crystals of bovine trypsin has been independently determined by X-ray diffraction to 1.35 Å resolution and by neutron diffraction to 2.1 Å resolution. A consensus model of the water molecule positions was obtained using oxygen positions identified in the electron density map determined by X-ray diffraction, which were verified by comparison to D2O—H2O difference neutron scattering density. Six of 184 water molecules in the X-ray structure, all with B-factors greater than 50 Å2, were found to be spurious after comparison with neutron results. Roughly two-thirds of the water of hydration expected from thermodynamic data for proteins was localized by neutron diffraction; approximately one-half of the water of hydration was located by X-ray diffraction. Polar regions of the protein are well hydrated, and significant D2O—H2O difference density is seen for a small number of water molecules in a second shell of hydration. Hydrogen bond lengths and angles calculated from unconstrained refinement of water positions are distributed about values typically seen in small molecule structures.Solvent models found in seven other bovine trypsin and trypsinogen and rat trypsin structures determined by X-ray diffraction were compared. Internal water molecules are well conserved in all trypsin structures including anionic rat trypsin, which is 65% homologous to bovine trypsin. Of the 22 conserved waters in trypsin, 19 were also found in trypsinogen, suggesting that they are located in regions of the apoprotein that are structurally conserved in the transition to the mature protein. Seven waters were displaced upon activation of trypsinogen. Water structure at crystal contacts is not generally conserved in different crystal forms. Three groups of integral structural water molecules are highly conserved in all solvent structures, including a spline of water molecules inserted between two β-strands, which may resemble an intermediate in the formation of β sheets during the folding of a protein.

Additional Material: 11 Ill.