The feasibility of stabilizing proteins towards proteolytic degradation was explored by engineeri... more The feasibility of stabilizing proteins towards proteolytic degradation was explored by engineering the primary proteolytic cleavage site(s). This novel approach does not require information on the 3-D structure of the native enzyme. As a model system, the extracellular lipase of Pseudomonas glumae was chosen, which is sensitive towards degradation by subtilisin-type proteases. The primary proteolytic cleavage in the lipase appeared to be located between amino acids serine 153 and histidine 154. Since subtilisins are known to show a preference towards amino acid residues surrounding the scissile bond, non-preferred amino acids were introduced in this area. Two concepts were tested: the introduction of arginine or glutamate residues (charge concept) and the introduction of proline residues (proline concept). Although the mutant lipases produced according to either of these concepts were still cleaved in the same area, they showed a considerably increased stability towards proteolytic degradation.
Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracel... more Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracellular aqueous milieu. Because the desorption from the membrane costs more energy than provided by two ATPs, the transporter probably only translocates the lipid to a partially hydrophilic site on its extracellular face. From this high-energy site, the lipid may efficiently move to the acceptor, which ideally is bound to the transporter, or, in the absence of an acceptor, fall back into the membrane. If the lipid originated from the cytosolic membrane surface, this represents lipid flop and is probably a side activity of the transporters.
In characterizing mutants and covalently inhibited complexes of Fusarium solani cutinase, which i... more In characterizing mutants and covalently inhibited complexes of Fusarium solani cutinase, which is a 197-residue lipolytic enzyme, 34 variant structures, crystallizing in 8 different crystal forms, have been determined, mostly at high resolution. Taking advantage of this considerable body of information, a structural comparative analysis was carried out to investigate the dynamics of cutinase. Surface loops were identified as the major flexible protein regions, particularly those forming the active-site groove, whereas the elements constituting the protein scaffold were found to retain the same conformation in all the cutinase variants studied. Flexibility turned out to be correlated with thermal motion. With a given crystal packing environment, a high flexibility turned out to be correlated with a low involvement in crystal packing contacts. The high degree of crystal polymorphism, which allowed different conformations with similar energy to be detected, made it possible to identify motions which would have remained unidentified if only a single crystal form had been available. Fairly good agreement was found to exist between the data obtained from the structural comparison and those from a molecular dynamics (MD) simulation carried out on the native enzyme. The crystallographic approach used in this study turned out to be a suitable tool for investigating cutinase dynamics. Because of the availability of a set of closely related proteins in different crystal environments, the intrinsic drawback of a crystallographic approach was bypassed. By combining several static pictures, the dynamics of the protein could be monitored much more realistically than what can be achieved on the basis of static pictures alone.
The feasibility of stabilizing proteins towards proteolytic degradation was explored by engineeri... more The feasibility of stabilizing proteins towards proteolytic degradation was explored by engineering the primary proteolytic cleavage site(s). This novel approach does not require information on the 3-D structure of the native enzyme. As a model system, the extracellular lipase of Pseudomonas glumae was chosen, which is sensitive towards degradation by subtilisin-type proteases. The primary proteolytic cleavage in the lipase appeared to be located between amino acids serine 153 and histidine 154. Since subtilisins are known to show a preference towards amino acid residues surrounding the scissile bond, non-preferred amino acids were introduced in this area. Two concepts were tested: the introduction of arginine or glutamate residues (charge concept) and the introduction of proline residues (proline concept). Although the mutant lipases produced according to either of these concepts were still cleaved in the same area, they showed a considerably increased stability towards proteolytic degradation.
Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracel... more Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracellular aqueous milieu. Because the desorption from the membrane costs more energy than provided by two ATPs, the transporter probably only translocates the lipid to a partially hydrophilic site on its extracellular face. From this high-energy site, the lipid may efficiently move to the acceptor, which ideally is bound to the transporter, or, in the absence of an acceptor, fall back into the membrane. If the lipid originated from the cytosolic membrane surface, this represents lipid flop and is probably a side activity of the transporters.
In characterizing mutants and covalently inhibited complexes of Fusarium solani cutinase, which i... more In characterizing mutants and covalently inhibited complexes of Fusarium solani cutinase, which is a 197-residue lipolytic enzyme, 34 variant structures, crystallizing in 8 different crystal forms, have been determined, mostly at high resolution. Taking advantage of this considerable body of information, a structural comparative analysis was carried out to investigate the dynamics of cutinase. Surface loops were identified as the major flexible protein regions, particularly those forming the active-site groove, whereas the elements constituting the protein scaffold were found to retain the same conformation in all the cutinase variants studied. Flexibility turned out to be correlated with thermal motion. With a given crystal packing environment, a high flexibility turned out to be correlated with a low involvement in crystal packing contacts. The high degree of crystal polymorphism, which allowed different conformations with similar energy to be detected, made it possible to identify motions which would have remained unidentified if only a single crystal form had been available. Fairly good agreement was found to exist between the data obtained from the structural comparison and those from a molecular dynamics (MD) simulation carried out on the native enzyme. The crystallographic approach used in this study turned out to be a suitable tool for investigating cutinase dynamics. Because of the availability of a set of closely related proteins in different crystal environments, the intrinsic drawback of a crystallographic approach was bypassed. By combining several static pictures, the dynamics of the protein could be monitored much more realistically than what can be achieved on the basis of static pictures alone.
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