Perceptually Augmented Simulator Design

Training simulators have proven their worth in a variety of fields, from piloting to air-traffic control to nuclear power station monitoring. Designing surgical simulators, however, poses the challenge of creating trainers that effectively instill not only high-level understanding of the steps to be taken in a given situation, but also the low-level "muscle-memory" needed to perform delicate surgical procedures. It is often impossible to build an ideal simulator that perfectly mimics the haptic experience of a surgical procedure, but by focussing on the aspects of the experience that are perceptually salient we can build simulators that effectively instill learning. We propose a general method for the design of surgical simulators that augment the perceptually salient aspects of an interaction. Using this method, we can increase skill-transfer rates without requiring expensive improvements in the capability of the rendering hardware or the computational complexity of the simulation. In this paper, we present our decomposition-based method for surgical simulator design, and describe a user-study comparing the training effectiveness of a haptic-search-task simulator designed using our method versus an unaugmented simulator. The results show that perception-based task decomposition can be used to improve the design of surgical simulators that effectively impart skill by targeting perceptually significant aspects of the interaction.

Oxidation of methionine residues in antithrombin. Effects on biological activity and heparin binding

Commercially available human plasma-derived preparations of the serine protease inhibitor antithrombin (AT) were shown to contain low levels of oxidation, and we sought to determine whether oxidation might be a means of regulating the protein's inhibitory activity. A recombinant form of AT, with similarly low levels of oxidation as purified, was treated with hydrogen peroxide in order to study the effect of oxidation, specifically methionine oxidation, on the biochemical properties of this protein. AT contains two adjacent methionine residues near the reactive site loop cleaved by thrombin (Met314 and Met315) and two exposed methionines that border on the heparin binding region of AT (Met17 and Met20). In forced oxidations with hydrogen peroxide, the methionines at 314 and 315 were found to be the most susceptible to oxidation, but their oxidation did not affect either thrombin-inhibitory activity or heparin binding. Methionines at positions 17 and 20 were significantly oxidized only at higher concentrations of peroxide, at which point heparin affinity was decreased. However at saturating heparin concentrations, activity was only marginally decreased for these highly oxidized samples of AT. Structural studies indicate that highly oxidized AT is less able to undergo the complete conformational change induced by heparin, most probably due to oxidation of Met17. Since this does not occur in less oxidized, and presumably more physiologically relevant, forms of AT such as those found in plasma preparations, oxidation does not appear to be a means of controlling AT activity.

Transgenically produced human antithrombin: structural and functional comparison to human plasma-derived antithrombin

Recombinant human antithrombin (rhAT) produced in transgenic goat milk was purified to greater than 99%. The specific activity of the rhAT was identical to human plasma-derived AT (phAT) in an in vitro thrombin inhibition assay. However, rhAT had a fourfold higher affinity for heparin than phAT. The rhAT was analyzed and compared with phAT by reverse phase high-performance liquid chromatography, circular dichroism, fluorophore-assisted carbohydrate electrophoresis (FACE), amino acid sequence, and liquid chromatography/mass spectrography peptide mapping. Based on these analyses, rhAT was determined to be structurally identical to phAT except for differences in glycosylation. Oligomannose structures were found on the Asn 155 site of the transgenic protein, whereas only complex structures were observed on the plasma protein. RhAT contained a GalNAc for galactose substitution on some N-linked oligosaccharides, as well as a high degree of fucosylation. RhAT was less sialylated than phAT and contained both N-acetylneuraminic and N-glycolylneuraminic acid. We postulate that the increase in affinity for heparin found with rhAT resulted from the presence of oligomannose-type structures on the Asn 155 glycosylation site and differences in sialylation.

Complete amino acid sequence of ananain and a comparison with stem bromelain and other plant cysteine proteases

The amino acid sequences of ananain (EC3.4.22.31) and stem bromelain (3.4.22.32), two cysteine proteases from pineapple stem, are similar yet ananain and stem bromelain possess distinct specificities towards synthetic peptide substrates and different reactivities towards the cysteine protease inhibitors E-64 and chicken egg white cystatin. We present here the complete amino acid sequence of ananain and compare it with the reported sequences of pineapple stem bromelain, papain and chymopapain from papaya and actinidin from kiwifruit. Ananain is comprised of 216 residues with a theoretical mass of 23464 Da. This primary structure includes a sequence insert between residues 170 and 174 not present in stem bromelain or papain and a hydrophobic series of amino acids adjacent to His-157. It is possible that these sequence differences contribute to the different substrate and inhibitor specificities exhibited by ananain and stem bromelain.

Removal of necrotic tissue with an ananain-based enzyme-debriding preparation

An enzymatic debriding preparation was formulated with purified enzyme derived from a crude pineapple stem extract. The primary component of this preparation was the sulfhydryl protease ananain which represented >/=85% of the proteolytic activity. The remaining proteolytic activity in the preparation was contributed by a co-purifying homologous cysteine protease comosain. Taken together these two proteases provided a protein purity of greater than 95% as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis. This ananain-based enzyme preparation exhibited both gelatinolytic and fibrinolytic activity in vitro. Ananain-based enzyme preparation was formulated in a hydrophilic cream vehicle at concentrations ranging from 115 to 260 U/gm vehicle. Ananain-based enzyme preparation formulated in this fashion is referred to as Vianain debriding agent. Vianain was applied to partial-thickness cutaneous burn wounds produced in the skin of domestic pigs. A maximum of two 4-hour applications of Vianain provided complete debridement of eschar from the partial-thickness burn wounds as judged by light and electron microscopic analyses of biopsy specimens harvested before and after debridement. Wounds debrided with Vianain exhibited more rapid reepithelialization as compared with wounds that were not debrided. Wounds on pigs that were hyperimmunized to ananain-based enzyme preparation before burning and debridement with Vianain exhibited a similar enhancement in reepithelialization as compared with wounds treated with vehicle alone. The capacity of Vianain to debride necrotic tissue was also evaluated in a guinea pig ischemic ulcer model. Full-thickness ischemic lesions were created on the back of guinea pigs. Vianain was applied to the hardened necrotic tissue for 6 hours per day for up to a maximum of 5 days. Complete debridement of these wounds was accomplished within 4 to 5 days. Treatment of ischemic cutaneous ulcerations in this animal model with two commercially available enzyme-debriding agents provided little or no debridement of the necrotic tissue. In vitro, Vianain treatment of surgically debrided human tissue samples, obtained from patients with burn injury or cutaneous ulcers, showed that the protease preparation was effective in rapidly digesting these necrotic tissues.

Antithrombin-heparin affinity reduced by fucosylation of carbohydrate at asparagine 155

The two human plasma antithrombin isoforms, alpha and beta, differ in glycosylation at asparagine 135. Only the alpha form carries carbohydrate at this position and has lower affinity for heparin than the beta form. We previously found additional heterogeneity in a recombinant N135Q antithrombin variant, evidenced by two isoforms with a 2-fold difference in heparin affinity [Turko, I. V., Fan, B., & Gettins, P. G. W. (1993) FEBS Lett. 335, 9-12]. To test whether this heterogeneity of heparin affinity results from specific glycosylation differences, we have determined the carbohydrate composition at the three remaining glycosylation sites, asparagine residues 96, 155, and 192, in each of the two N135Q isoforms, by a combination of peptide fragmentation and electrospray mass spectrometry. Patterns of glycosylation at residues 96 and 192 were similar for each isoform and showed the presence of mono-, bi-, and triantennary complex carbohydrate, as well as fucosylation of all types of chains. At position 155, however, there was a marked difference between the isoforms, with the form with lower heparin affinity being 97% fucosylated at this position, whereas the form with higher affinity for heparin was not fucosylated. Other differences in carbohydrate type showed no strong correlation between the two isoforms. We conclude that formation of the two heparin-affinity isoforms of N135Q antithrombin results from the specific difference in fucosylation at residue 155, which may result in different structural properties of the carbohydrate. Consistent with these findings was the elimination of heparin-affinity heterogeneity in a double N135Q-N155Q variant antithrombin. It is possible that fucosylation of antithrombin may occur in vivo as a means of modifying the physiological properties of the antithrombin through alteration of the amount of antithrombin bound to surface heparin-like species.

Recombinant human thyroid stimulating hormone: development of a biotechnology product for detection of metastatic lesions of thyroid carcinoma

We have genetically engineered a cell line, and developed a reproducible process, for the expression and purification of biologically active recombinant human thyroid stimulating hormone (rhTSH).rhTSH was expressed by co-transfecting a human alpha-subunit cDNA with a human beta-subunit partial genomic clone into Chinese Hamster Ovary (CHO) cells. Stable transfectants which expressed high levels of rhTSH were selected, and subsequently cultured on microcarrier beads. The rhTSH-containing media, produced under serum-free conditions, was clarified and purified by a combination of ion exchange, dye and gel filtration chromatographies. Individual step recoveries were greater than 90% with the exception of a very conservative pooling of the final gel filtration step (78% recovery) that resulted in a cumulative yield of 54% for the purification process. Purity of the final bulk material was judged to be > 99% by SDS polyacrylamide gel electrophoresis (SDS-PAGE), reverse phase HPLC, and size exclusion chromatography. Initial characterization of the oligosaccharide composition indicated the presence of partially sialylated bi- and triantenary complex oligosaccharides. Purified rhTSH was active in a thyroid membrane bioactivity assay with a specific activity of 8.2 IU/mg. The in vivo activity of rhTSH in cynomolgus monkeys appeared to be equal to or greater than that reported for bovine TSH (bTSH) in human subjects. The rapid clearance phase half-life of rhTSH was approximately 35 minutes while the post-distribution phase half life was approximately 9.8 hours. Furthermore, the monkeys showed cumulative increases in minimum plasma rhTSH levels when given three daily intramuscular (IM) rhTSH injections; a phenomenon not observed when bTSH had been administered to humans. The rhTSH showed no evidence of toxic or adverse effects when administered at doses up to 7.2 IU/kg and 0.52 IU/kg in rat and monkey, respectively. These are 50X and 4X multiples of the bTSH doses of 0.143 IU/kg (10 IU/70kg) previously administered to humans.

Characterization of the microheterogeneity of recombinant primate prolactin: implications for posttranslational modifications of the hormone in vivo

Recombinant baboon and monkey prolactins were expressed in murine C127 cells. The hormones were purified from the conditioned media of these cells using a combination of cation, anion, and gel filtration chromatographies. This purification scheme provided approximately a 20-fold purification of the proteins with a 40% cumulative yield. Sodium dodecyl sulfate gel electrophoresis of the purified hormones in conjunction with Coomassie blue staining and immunoblotting procedures revealed three major prolactin-related bands with molecular weights corresponding to Mr 16,000, 23,000, and 27,000. Based on these analyses the samples were judged to be greater than 90% pure. Amino terminal sequence analysis of the purified baboon and monkey hormones provided three distinct prolactin-related sequences for each preparation. The predominant sequence corresponded to the predicted amino terminal sequences of the hormones which began with leucine at position 1. Two minor sequences, individually representing approximately 10-20% of the total population, were also identified; one starting at position 11 and the other at position 133. Carbohydrate compositional analysis of the proteins suggested that greater than 50% of the population were glycosylated with a fucosylated complex oligosaccharide. Analysis of the specific bioactivity of the recombinant hormones in the Nb2 cell proliferation assay showed them to be comparable to the NIH and WHO human pituitary-derived standards.

Transgenic expression of a variant of human tissue-type plasminogen activator in goat milk: purification and characterization of the recombinant enzyme

A glycosylation variant of human tissue-type plasminogen activator (tPA) designated longer-acting tissue-type plasminogen activator (LAtPA) was extensively purified from the milk of a transgenic goat by a combination of acid fractionation, hydrophobic interaction chromatography and immunoaffinity chromatography. This scheme provided greater than 8,000-fold purification of the protein, a cumulative yield of 25% and purity greater than 98% as judged by SDS gel electrophoresis. SDS gel electrophoresis revealed that the transgenic enzyme was predominantly the "two chain" form of the protease. The specific activity of the purified transgenic protein, based on the average of the values obtained for three different preparations, was 610,000 U/mg as judged by amidolytic activity assay. This was approximately 84% of the value observed for the recombinant enzyme produced in mouse C127 cells. Analysis of the transgenic protein indicated that it had a significantly different carbohydrate composition from the recombinant enzyme produced in C127 cells. Molecular size analysis of the oligosaccharides from the transgenic and C127 cell-derived LAtPA preparations confirmed their differences and showed that the mouse cell-derived preparation contained larger, complex-type N-linked oligosaccharide structures than the material produced in goat mammary tissue.

Comparison of the autolyzed and unautolyzed forms of mu- and m-calpain from bovine skeletal muscle

Bovine skeletal muscle mu- and m-calpain autolyze when incubated with Ca2+. During the first 30 to 300 s, autolysis: (1) has little effect on the specific proteolytic activity of either mu- or m-calpain when assayed at 5 mM Ca2+; and (2) produces two new proteolytically active forms of calpain in addition to the original mu- and m-calpain. The four proteolytically active forms of calpain are: (1) autolyzed mu-calpain, having polypeptide subunits of 76 and 18 kDa and requiring 0.60 microM Ca2+ for half-maximal activity; (2) mu-calpain with 80- and 28-kDa subunits and requiring 7.1 microM Ca2+ for half-maximal activity; (3) autolyzed m-calpain with 78- and 18-kDa subunits and requiring 180 microM Ca2+ for half-maximal activity; and (4) m-calpain with 80- and 28-kDa subunits and requiring 1000 microM Ca2+ for half-maximal activity. All four forms of the calpains have similar pH optima (7.4 to 7.6) and almost identical circular dichroism spectra in the far ultraviolet (all four have little secondary structure with 26-30% alpha-helix and less than 10% beta-sheet structure). Autolyzed mu- and unautolyzed mu-calpain are fully activated proteolytically by Mn2+ with activity starting at 125 microM Mn2+. Autolyzed m-calpain is also activated by Mn2+ up to 80% of the maximum proteolytic activity obtained with Ca2+; Mn2+ activation begins at 320 microM Mn2+. Unautolyzed m-calpain has only 6 to 8% as much activity in the presence of Mn2+ as it does in the presence of Ca2+. Autolysis increases the axial ratios of the calpains from 3.5 to 4.6 for mu-calpain and from 3.7 to 5.0 for m-calpain (assuming 20% hydration). The estimated length of the calpain molecules increases by 13% upon autolysis from 73 to 84 A for mu-calpain and from 76 to 90 A for m-calpain (assuming 20% hydration). The autolyzed calpains elute after their unautolyzed counterparts off a DEAE-ion exchange column. Because autolyzed forms of the calpains are not found in DEAE elution profiles of cell extracts, bovine skeletal muscle cells must contain very little (less than 5% of total calpain) or none of the autolyzed form of the calpains.

Chicken skeletal muscle has three Ca2+-dependent proteinases

Chicken breast muscle has three Ca2+-dependent proteinases, two requiring millimolar Ca2+ (m-calpain and high m-calpain) and one requiring micromolar Ca2+ (mu-calpain). High m-calpain co-purifies with mu-calpain through successive DEAE-cellulose (steep gradient), phenyl-Sepharose, octylamine agarose, and Sephacryl S-300 columns, but elutes after mu-calpain when using a shallow KCl gradient to elute a DEAE-cellulose column. The mu- and m-calpains have 80 and 28 kDa polypeptides and are analogous to the mu- and m-calpains that have been purified from bovine, porcine and rabbit skeletal muscle. High m-calpain, which seems to be a new Ca2+-dependent proteinase, is still heterogeneous after the DEAE-cellulose column eluted with a shallow KCl gradient. Additional purification through two successive HPLC-DEAE columns and one HPLC-SW-4000 gel permeation column produces a fraction having six major polypeptides and 6-8 minor polypeptides on SDS-PAGE. A 74-76 kDa polypeptide in this fraction reacts in Western blots with monospecific, polyclonal anti-calpain antibodies that react with both the 80 kDa and the 28 kDa polypeptides of mu- or m-calpain. High m-calpain also is related to mu- and m-calpain in that it causes the same limited digestion of skeletal muscle myofibrils, has a similar pH optimum near pH 7.9-8.4, requires Ca2+ for activity, and reacts with the calpain inhibitor, calpastatin, and a variety of serine and cysteine proteinase inhibitors in a manner identical to mu- and m-calpain. High m-calpain differs from mu- and m-calpain in its elution off DEAE-cellulose columns and its requirement of 3800 microM Ca2+ for one-half maximal activity compared with 5.35 microM Ca2+ for mu-calpain and 420 microM Ca2+ for m-calpain. The physiological significance of high m-calpain in unclear. The presence of mu-calpain in chicken breast muscle suggests that all skeletal muscles contain both mu- and m-calpain, although the relative proportions of these two proteinases may vary in different species.

Immunofluorescent localization of the Ca2+-dependent proteinase and its inhibitor in tissues of Crotalus atrox

The native 108,000 dalton Ca2+-dependent proteinase (CDP) and its 115,000 dalton protein inhibitor (CDPI) were purified from bovine skeletal muscle using native polyacrylamide gel electrophoresis and were used to elicit antibody production in rabbits and BALB/c mice. Polyclonal antibodies were purified as IgG fractions by column chromatography; monoclonal antibodies were produced by the hybridoma technique. Indirect immunofluorescence localization of CDP and CDPI in tissues of Crotalus atrox show both proteins to be ubiquitous. Both occur in the cytoplasm and are absent from the cell membrane and the nucleus; CDPI is also present in the I-band of skeletal muscle.

A high molecular weight peptide hydrolase in erythrocytes

1. A peptide hydrolase has been partially purified from the soluble fraction of erythrocyte lysates. 2. The enzyme has a molecular weight of approximately 600,000 and hydrolyses the chymotrypsin substrate glutaryl-Gly-Gly-Phe-7-amido-4-methylcoumarin (pH optimum 7.0) and the trypsin substrate CBZ-Gly-Gly-Arg-2-naphthylamide. The two activities could not be separated by the purification procedure used. 3. The activity towards glutaryl-Gly-Gly-Phe-7-amido-4-methylcoumarin in rat reticulocytes was four times that in mature erythrocytes. 4. Activity was abolished by 10 microM p-hydroxymercuriphenylsulphonic acid.