Quantitative sensory testing of intraoral open wounds.

Wound healing is an important aspect of oral and maxillofacial surgery. Positive sensory signs (allodynia, hyperalgesia) and negative sensory signs (hypoesthesia, hypoalgesia) may be encountered. Quantitative sensory testing (QST) has moved from bench to bedside for the detection, therapy selection and monitoring the recovery of individuals with sensory disturbances. Tracking somatosensory changes during normal and abnormal wound healing has not previously been reported. This report presents data obtained by a novel, automated, non-contact psychophysical method for assessment of wound sensitivity after standardized oral mucosal biopsy. By directing graded air puffs towards palatal biopsy wounds, thresholds for sensory detection, pain detection and pain tolerance were repeatedly assessed across 19 days, demonstrating high reliability. Participants recorded daily spontaneous and chewing-evoked maximum pains. Pain detection and tolerance thresholds increased linearly across time. Comparison between air puff evoked pain detection threshold and chewing-evoked pain demonstrated a strong correlation. Thus, for the first time, this study tracked the time course of somatosensory sensitivity of wounds induced by oral biopsies. The psychophysical data on wound healing obtained by this automated, contact-free stimulation method can be utilized as a surrogate marker for clinical pain improvements and standardized assessment of intraoral pain sensitivity, for example in oral mucositis.

Energetics of coiled coil folding: the nature of the transition states.

Coiled coils are simple models for studying the association of two polypeptide chains to form a folded protein. Previous work has shown that the folding of a coiled coil can be described by a two-state transition between two unfolded monomeric peptide chains and a folded coiled coil dimer. Here we report the thermodynamic activation parameters for the folding and unfolding of two unrelated coiled coils: C62GCN4 and A(2). C62GCN4 corresponds to the 62 C-terminal residues of yeast transcription factor GCN4. The peptide forms a dimeric coiled coil through its 33 C-terminal residues. A(2) is a designed 30-residue dimeric coiled coil whose folding is induced by low pH [Dürr, E., Jelesarov, I., and Bosshard, H. R. (1999) Biochemistry 38, 870-880]. Folding and unfolding were assessed under identical native buffer conditions so that the microscopic reversibility applied and the transition state was the same for folding and unfolding. The time course of folding was followed from the self-quenching of a C-terminal fluorescent label (Texas Red). The overall folding of both peptides is enthalpy-driven and opposed by a loss of entropy. The main energetic changes occur after the system has passed the transition state. In the folding of C62GCN4, only 10-20% of the heat capacity change is attained between the monomeric state and the dimeric transition state. For coiled coil A(2), the fractional heat capacity change preceding the transition state is 30-40%. The results indicate that the activated states of folding of coiled coils are not well structured and differ considerably from the folded coiled coil conformation. These findings are in agreement with a rate-limiting transition state in which the coiled coil helices and the hydrophobic coiled coil interface are poorly developed.

Liposome-assisted selective polycondensation of alpha-amino acids and peptides.

The main question of this paper is whether and to what extend lipid bilayers can aid in the polycondensation of amino acids and peptides. This means in particular how such bilayers can favor the selection of certain sequences out of a large number of theoretical possible ones. In a first series of experiments we started from a library of Trp-containing dipeptides of the type Trp-X where X is an amino acid residue; and we could show that, when adding this mixture to the POPC liposomes containing a hydrophobic quinoline condensing agent (EEDQ), only the hydrophobic Trp-Trp dipeptide is selected out by the liposomes and transformed into a longer oligomer. Trp-oligomers up to 29 monomers long (water insoluble) could be obtained by using the matrix support of liposomes. Mixed POPC/DDAB liposomes (positive charge) were used to produce co-oligopeptides that contain Trp and Glu residues in the same sequence. Arg/Trp and His/Trp containing sequences were obtained in presence of negatively charged liposomes (mixed POPC/DOPA-liposomes). The polycondensation of racemic NCA-amino acids has been studied to clarify if homochiral sequences are produced preferentially in presence or absence of liposomes. LC-MS and isotope labeling of the L-amino acid, participating in the polymerization reaction achieved this on the level of a direct product analysis. So the individual stereoisomer distribution up to a polymerization degree of 10 (in the case of Trp) could be determined. The data for Trp and other amino acids (Leu, Ile) and amino acid mixtures (Trp/Leu, Trp/Ile, Leu/Ile and Trp/Leu/Ile) show that homochiral sequences are produced preferentially if compared with a random (Bernoulli) distribution.