Biomedical subjects

Kai Hilpert

Publications and source records attributed to Kai Hilpert.

8 recordsLinked to original sources

PubMed2006

Sequence requirements and an optimization strategy for short antimicrobial peptides.

Short antimicrobial host-defense peptides represent a possible alternative as lead structures to fight antibiotic resistant bacterial infections. Bac2A is a 12-mer linear variant of the naturally occurring bovine host defense peptide, bactenecin, and demonstrates moderate, broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria as well as against the yeast Candida albicans. With the assistance of a method involving peptide synthesis on a cellulose support, the primary sequence requirements for antimicrobial activity against the human pathogen Pseudomonas aeruginosa of 277 Bac2A variants were investigated by using a luciferase-based assay. Sequence scrambling of Bac2A led to activities ranging from superior or equivalent to Bac2A to inactive, indicating that good activity was not solely dependent on the composition of amino acids or the overall charge or hydrophobicity, but rather required particular linear sequence patterns. A QSAR computational analysis was applied to analyze the data resulting in a model that supported this sequence pattern hypothesis. The activity of selected peptides was confirmed by conventional minimal inhibitory concentration (MIC) analyses with a panel of human pathogen bacteria and fungi. Circular-dichroism (CD) spectroscopy with selected peptides in liposomes and membrane depolarization assays were consistent with a relationship between structure and activity. An additional optimization process was performed involving systematic amino acid substitutions of one of the optimal scrambled peptide variants, resulting in superior active peptide variants. This process provides a cost and time effective enrichment of new candidates for drug development, increasing the chances of finding pharmacologically relevant peptides.

Amino Acid Sequence↗

PubMed2005

High-throughput generation of small antibacterial peptides with improved activity.

Cationic antimicrobial peptides are able to kill a broad variety of Gram-negative and Gram positive bacteria and thus are good candidates for a new generation of antibiotics to treat multidrug-resistant bacteria. Here we describe a high-throughput method to screen large numbers of peptides for improved antimicrobial activity. The method relies on peptide synthesis on a cellulose support and a Pseudomonas aeruginosa strain that constitutively expresses bacterial luciferase. A complete substitution library of 12-amino-acid peptides based on a linearized variant (RLARIVVIRVAR-NH(2)) of the bovine peptide bactenecin was screened and used to determine which substitutions at each position of the peptide chain improved activity. By combining the most favorable substitutions, we designed optimized 12-mer peptides showing broad spectrum activities with minimal inhibitory concentrations (MIC) as low as 0.5 microg/ml against Escherichia coli. Similarly, we generated an 8-mer substituted peptide that showed broad spectrum activity, with an MIC of 2 microg/ml, against E. coli and Staphylococcus aureus.

Amino Acid Sequence↗

PubMed2005

Complete substitutional analysis of a sunflower trypsin inhibitor with different serine proteases.

Here we present a method to simultaneously characterize and/or optimize both the binding loop towards the protease and a cysteine-stabilized scaffold. The small peptidic sunflower trypsin inhibitor (SFTI-1) was chosen as a model system for these experiments. The inhibitor was investigated for positional specificity against trypsin, elastase and proteinase K using complete substitutional analyses based on cellulose-bound peptide spot synthesis. Inhibitor variants optimized for elastase or proteinase K inhibition by several rounds of substitutional analyses exhibit K(i) values in the micromolar range and high specificity for the corresponding protease. The results of this easy-to-perform assay can be used to design an improved peptide library using classical methods.

Amino Acid Sequence↗

PubMed2005

Unraveling sub-site specificities of peptidic serine protease inhibitors by substitutional and structural analysis.

The interaction of peptidic inhibitors with serine proteases is investigated using peptide spot synthesis on cellulose sheets. This method permits a highly parallel analysis of subsite specificities and an optimization of peptidic inhibitors towards higher affinity and specificity for a given target protease. Information from crystal structures of corresponding protease/inhibitor complexes may help to explain the observed binding pattern.

Amino Acid Substitution↗

PubMed2004

Crystallization and preliminary x-ray analysis of complexes of porcine pancreatic elastase with two natural inhibitors.

Two different natural protease inhibitors, the squash inhibitor MCEI III and the third domain of turkey ovomucoid inhibitor OMTKY3, were crystallized in complexes with porcine pancreatic elastase (PPE). About 700 conditions were screened altogether. Crystals of the complex between MCEI III and PPE were grown in citrate buffer with and without ammonium acetate. X-ray diffraction data were collected to 1.9 angstroms resolution at room temperature using synchrotron radiation. The crystals belong to space group P2(1), with unit-cell parameters a = 49.17, b = 44.59, c = 67.08 angstroms, beta = 110.97 degrees. Crystals of the OMTKY3/PPE complex were obtained in the presence of ammonium sulfate, MES buffer and polyethylene glycol monomethylether (PEG). These crystals of this complex diffracted to 2.1 angstroms resolution and belongs to space group I222, with unit-cell parameters a = 84.58, b = 84.61, c = 89.92 angstroms and diffracted to 2.2 angstroms resolution. The diffraction data were collected using a conventional rotating anode X-ray generator at room temperature. In both cases the presence of inhibitor in the crystals was confirmed by crystallography.

Amino Acid Sequence↗

PubMed2003

Design and characterization of a hybrid miniprotein that specifically inhibits porcine pancreatic elastase.

Studying protease/peptide inhibitor interactions is a useful tool for understanding molecular recognition in general and is particularly relevant for the rational design of inhibitors with therapeutic potential. An inhibitory peptide (PMTLEYR) derived from the third domain of turkey ovomucoid inhibitor and optimized for specific porcine pancreatic elastase inhibition was introduced into an inhibitor scaffold to increase the proteolytic stability of the peptide. The trypsin-specific squash inhibitor EETI II from Ecballium elaterium was chosen as the scaffold. The resulting hybrid inhibitor HEI-TOE I (hybrid inhibitor from E. elaterium and the optimized binding loop of the third domain of turkey ovomucoid inhibitor) shows a specificity and affinity to porcine pancreatic elastase similar to the free inhibitory peptide but with significantly higher proteolytic stability. Isothermal titration calorimetry revealed that elastase binding of HEI-TOE I occurs with a small unfavorable positive enthalpy contribution, a large favorable positive entropy change, and a large negative heat capacity change. In addition, the inhibitory peptide and the hybrid inhibitor HEI-TOE I protected endothelial cells against degradation following treatment with porcine pancreatic elastase.

Amino Acid Sequence↗

PubMed2003

Structure of a hybrid squash inhibitor in complex with porcine pancreatic elastase at 1.8 A resolution.

The crystal structure of porcine pancreatic elastase in complex with a hybrid squash inhibitor (HEI-TOE I; 28 amino acids) has been determined to a resolution of 1.8 A. To construct the hybrid inhibitor, the trypsin-binding loop of the squash inhibitor from Ecballium elaterium was substituted by the sequence of a peptide that was derived from the third domain of the turkey ovomucoid inhibitor and was optimized to inhibit porcine pancreatic elastase. This modification of the squash inhibitor changed its specificity for trypsin to a specificity for porcine pancreatic elastase. Specific interactions of this hybrid inhibitor with porcine pancreatic elastase and the differences from the interactions of the ovomucoid inhibitor with human leukocyte elastase are discussed. The binding loop of the inhibitor adopts a 'canonical' conformation and the scissile bond Leu-Glu remains intact.

Amino Acid Sequence↗

PubMed2002

Crystallization and preliminary X-ray analysis of the complex of porcine pancreatic elastase and a hybrid squash inhibitor.

A hybrid inhibitor consisting of the scaffold of a squash-type inhibitor and a specific inhibitory peptide optimized from the third domain of ovomucoid inhibitor from turkey against porcine pancreatic elastase was synthesized by peptide synthesis. The complex formed by this hybrid inhibitor and the porcine pancreatic elastase was crystallized using the hanging-drop method with citrate in the crystallization solution. The space group was determined to be P2(1)2(1)2(1), with unit-cell parameters a = 56.33, b = 56.44, c = 72.76 A. A complete X-ray diffraction data set was collected under cryogenic conditions to 1.8 A.

Animals↗