Cysteine pairing in the glycoprotein IIbIIIa antagonist kistrin using NMR, chemical analysis, and structure calculations

The pairing of the cysteines in disulfide bonds was investigated for the 68-residue RGD-containing protein kistrin, a potent antagonist of the integrin GP IIbIIIa and an inhibitor of platelet aggregation. Kistrin belongs to a family of homologous proteins found in snake venoms termed disintegrins, all of which have a cysteine content. The disulfide pairing of the 12 cysteines was investigated by chemical analysis, NMR spectroscopy, and distance geometry calculations. The data show that the disulfide pairs are 4-19, 6-14, 13-36, 27-33, 32-57, and 45-64. The various means for assigning the disulfide bonds are described, and the results are compared with the cysteine pairings reported for other disintegrin proteins.

Weyers' ulnar ray/oligodactyly syndrome and the association of midline malformations with ulnar ray defects

We describe a two generation family with variable ulnar and radial ray reduction and midline craniofacial abnormalities. The features suggest a diagnosis of Weyers' ulnar ray/oligodactyly syndrome originally described in two isolated cases. Syndromes of ulnar ray reduction are briefly reviewed and the relationship between limb bud and midline development discussed.

Humanization of an anti-p185HER2 antibody for human cancer therapy

The murine monoclonal antibody mumAb4D5, directed against human epidermal growth factor receptor 2 (p185HER2), specifically inhibits proliferation of human tumor cells overexpressing p185HER2. However, the efficacy of mumAb4D5 in human cancer therapy is likely to be limited by a human anti-mouse antibody response and lack of effector functions. A "humanized" antibody, humAb4D5-1, containing only the antigen binding loops from mumAb4D5 and human variable region framework residues plus IgG1 constant domains was constructed. Light- and heavy-chain variable regions were simultaneously humanized in one step by "gene conversion mutagenesis" using 311-mer and 361-mer preassembled oligonucleotides, respectively. The humAb4D5-1 variant does not block the proliferation of human breast carcinoma SK-BR-3 cells, which overexpress p185HER2, despite tight antigen binding (Kd = 25 nM). One of seven additional humanized variants designed by molecular modeling (humAb4D5-8) binds the p185HER2 antigen 250-fold and 3-fold more tightly than humAb4D5-1 and mumAb4D5, respectively. In addition, humAb4D5-8 has potency comparable to the murine antibody in blocking SK-BR-3 cell proliferation. Furthermore, humAb4D5-8 is much more efficient in supporting antibody-dependent cellular cytotoxicity against SK-BR-3 cells than mumAb4D5, but it does not efficiently kill WI-38 cells, which express p185HER2 at lower levels.

CD20 and CD5 expression in B-chronic lymphocytic leukemia

In order to quantitate a previously noted decrease in CD20 fluorescence intensity (FI) on B-CLL lymphocytes, binding capacities [BC x 10(3) +/- 1SD = number of antibodies bound per cell] were calculated. The mean (N = 5) BC x 10(3) +/- 1SD of CD20 reagents for normal B-PBL and B-CLL lymphocytes confirmed this observation. B-PBL and B-CLL were 56 +/- 11 and 61 +/- 14, and 19 +/- 15 and 18 +/- 16, respectively, for Leu 16 and B1. Although adequate compensation standards for the determination of CD5 and CD20 coexpression are not available, qualitatively, the density of CD5 on both normal B-PBL and B-CLL is less compared to the expression of CD5 by normal T cells. CD5 expression on B-CLL seems to be linked to the lower levels of CD20, whereas CD5 expression may appear to be absent on CLL lymphocytes expressing normal levels of CD20. Levels of CD20 in B-CLL suggest involvement of one or two genes (alleles) whose decreased expression may be linked to CD5 expression.

Development of humanized bispecific antibodies reactive with cytotoxic lymphocytes and tumor cells overexpressing the HER2 protooncogene

The HER2 protooncogene encodes a 185-kD transmembrane phosphoglycoproteins, human epidermal growth factor receptor 2 (p185HER2), whose amplified expression on the cell surface can lead to malignant transformation. Overexpression of HER2/p185HER2 is strongly correlated with progression of human ovarian and breast carcinomas. Recent studies have shown that human T cells can be targeted with bispecific antibody to react against human tumor cells in vitro. We have developed a bispecific F(ab')2 antibody molecule consisting of a humanized arm with a specificity to p185HER2 linked to another arm derived from a murine anti-CD3 monoclonal antibody that we have cloned from UCHT1 hybridoma. The antigen-binding loops for the anti-CD3 were installed in the context of human variable region framework residues, thus forming a fully humanized BsF(ab')2 fragment. Additional variants were produced by replacement of amino acid residues located in light chain complementarity determining region 2 and heavy chain framework region 3 of the humanized anti-CD3 arm. Flow cytometry analysis showed that the bispecific F(ab')2 molecules can bind specifically to cells overexpressing p185HER2 and to normal human peripheral blood mononuclear cells bearing the CD3 surface marker. In additional experiments, the presence of bispecific F(ab')2 caused up to fourfold enhancement in the cytotoxic activities of human T cells against tumor cells overexpressing p185HER2 as determined by a 51Cr release assay. These bispecific molecules have a potential use as therapeutic agents for the treatment of cancer.

High Level Escherichia coli Expression and Production of a Bivalent Humanized Antibody Fragment

Many clinical uses of antibodies will require large quantities of fragments which are bivalent and humanized. We therefore attempted to generate humanized F(ab')2 fragments by secretion from E. coli. Titers of 1-2 g l-1 of soluble and functional Fab' fragments have been routinely achieved as judged by antigen-binding ELISA. Surprisingly, this high expression level of Fab' in the periplasmic space of E. coli does not drive dimerization. However, we have developed a protocol to directly and efficiently recover Fab' with the single hinge cysteine in the free thiol state, allowing F(ab')2 formation by chemically-directed coupling in vitro. The E. coli derived humanized F(ab')2 fragment is indistinguishable from F(ab')2 derived from limited proteolysis of intact antibody in its binding affinity for the antigen, p185HER2, and anti-proliferative activity against the human breast tumor cell line, SK-BR-3, which over-expresses p185HER2. This system makes E. coli expression of bivalent antibody fragments for human therapy (or other uses) practical.

Organising a continence advisory service

Modern surgical techniques have greatly improved the treatment of incontinence, but there remains a large number of patients for whom conservative management will be necessary. This paper reports the appointment of a continence adviser 10 years ago, and describes the subsequent development of a District Continence Advisory Service. Experience has shown that this appointment is essential, not only in terms of facilitating the service, but also as a means of ensuring cost efficiency.

Probing the mechanism and improving the rate of substrate-assisted catalysis in subtilisin BPN'

A mutant of the serine protease, subtilisin BPN', in which the catalytic His64 is replaced by Ala (H64A), is very specific for substrates containing a histidine, presumably by the substrate-bound histidine assisting in catalysis [Carter, P., & Wells, J.A. (1987) Science (Washington, D.C.) 237, 394-399]. Here we probe the catalytic mechanism of H64A subtilisin for cleaving His and non-His substrates. We show that the ratio of aminolysis to hydrolysis is the same for ester and amide substrates as catalyzed by the H64A subtilisin. This is consistent with formation of a common acyl-enzyme intermediate for H64A subtilisin, analogous to the mechanism of the wild-type enzyme. However, the catalytic efficiencies (kcat/KM) for amidase and esterase activities with His-containing substrates are reduced by 5000-fold and 14-fold, respectively, relative to wild-type subtilisin BPN, suggesting that acylation is more compromised than deacylation in the H64A mutant. High concentrations of imidazole are much less effective than His substrates in promoting hydrolysis by the H64A variant, suggesting that the His residue on the bound (not free) substrate is involved in catalysis. The reduction in catalytic efficiency kcat/KM for hydrolysis of the amide substrate upon replacement of the oxyanion stabilizing asparagine (N155G) is only 7-fold greater for wild-type than H64A subtilisin. In contrast, the reductions in kcat/KM upon replacement of the catalytic serine (S221A) or aspartate (D32A) are about 3000-fold greater for wild-type than H64A subtilisin, suggesting that the functional interactions between the Asp32 and Ser221 with the substrate histidine are more compromised in substrate-assisted catalysis.(ABSTRACT TRUNCATED AT 250 WORDS)

RO 23-6457 prolongs survival of vascularized allografts in rodents and primates

The ability of RO 23-6457, a retinoid compound with marked in vitro immunosuppressive properties, to prolong vascularized allografts was examined in several in vivo transplantation models. In the murine heterotopic heart model, efficacy was shown in two H-2 incompatible strain combinations, with indefinite graft survival at some doses. In the rat heterotopic heart model, oral administration prolonged Wistar-Furth grafts in Lewis hosts an average of 1 week, with no long-term survivors at a variety of doses. Given subcutaneously, grafts were further prolonged, but the compound proved toxic. In a bilaterally nephrectomized renal transplant model in cynomolgus monkeys treated intravenously at a dose of 2 mg/kg/day, host survival was prolonged to 18, 32, 33, and 74 days, compared with 11, 11, 12, 13, and 26 days in untreated controls (P less than 0.05 by rank-sum testing). The three shorter surviving recipients died from anorexia and weight loss with normal renal function, while the longest survivor rejected its kidney when exhaustion of iv sites precluded further treatment. The toxic effects of the compound resemble the syndrome of hypervitaminosis A. RO 23-6457 will prolong graft survival as a single agent, justifying further preclinical testing and efforts to reduce toxicity.

Functional interaction among catalytic residues in subtilisin BPN'

Variants of the serine protease, subtilisin BPN', in which the catalytic triad residues (Ser-221, His-64, and Asp-32) are replaced singly or in combination by alanine retain activities with the substrate N-succinyl-L-Ala-L-Ala-L-Pro-L-Phe-p-nitroanilide (sAAPF-pna) that are at least 10(3) to 10(4) above the non-enzymatic rate [Carter, P., Wells, J.A. Nature (London) 322:564-568, 1988]. A possible source of the residual activity was the hydrogen bond with the N delta 2 of Asn-155 that helps to stabilize the oxyanion generated in the tetrahedral transition state during amide bond hydrolysis by the wild-type enzyme. Replacing Asn-155 by Gly (N155G) lowers the turnover number (kcat) for sAAPF-pna by 150-fold with virtually no change in the Michaelis constant (KM). However, upon combining the N155G and S221A mutations to give N155G:S221A, kcat is actually 5-fold greater than for the S221A enzyme. Thus, the catalytic role of Asn-155 is dependent upon the presence of Ser-221. The residual activity of the N155G:S221A enzyme (approximately 10(4)-fold above the uncatalyzed rate) is not an artifact because it can be completely inhibited by the third domain of the turkey ovomucoid inhibitor (OMTKY3), which forms a strong 1:1 complex with the active site. The mutations N155G and S221A individually weaken the interaction between subtilisin and OMTKY3 by 1.8 and 2.0 kcal/mol, respectively, and in combination by 2.1 kcal/mol. This is consistent with disruption of stabilizing interactions around the reactive site carbonyl of the OMTKY3 inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Plunging ranula: literature review and report of three cases

Three cases of plunging ranula are described and the literature is reviewed. In many cases, a plunging ranula is iatrogenic and follows surgery to an oral ranula. In the cases presented, the cervical swelling was associated with prolongations of sublingual gland into or through the mylohyoid muscle. All patients were cured by partial or total excision of the sublingual gland.

Antigenic expression of B-cell chronic lymphocytic leukemic lymphocytes

A flow cytometric analysis of lymphocytes in B-cell chronic lymphocytic leukemia (B-CLL) samples and in monocyte-depleted and T-cell-depleted normal peripheral blood (B-PBL) samples was undertaken using 129 reagents from the blind panel (BP) and 72 reagents from the cluster designation (CD) panel obtained from the Fourth International Leucocyte Differentiation Conference and Workshop, B-Cell Section. After determining the average mean channel fluorescence and the average percentage of positive cells for the B-CLL and the normal B-PBL preparations, a combined ratio and difference analysis was performed for each monoclonal antibody reactivity. This analysis confirmed the intense expression of class II antigens on B-CLL and the preferential expression of CD19, CD20, CD23 and CD24 antigens. In addition, three new clustered and three new unclustered antigens were also preferentially expressed on B-CLL lymphocytes. Cluster analysis of these differences suggests the existence of at least three overlapping immunophenotypic subpopulations, composed of CD19, CD20, CD21, CD22, CD23, CD24, CD75, CD76 and CDw78.

The structures of human C1r and C1s and their relationship to other serine proteases

The recent sequencing of the C1 subcomponents has allowed comparison with other molecules of homologous primary structure. Where tertiary structures are available for at least one member of the family it is possible to make further progress by modelling the amino acid sequence of the complement protein into the three-dimensional coordinates of the directly determined structure, thereby obtaining an approximation of the structure of the complement protein. Molecular modelling allows structure-function relationships to be explored and suggests further experiments that may be amenable to techniques such as site-directed mutagenesis.

Molecular defects of the C1-inhibitor gene in hereditary angioedema

Family studies of hereditary angioedema are discussed with particular emphasis on the molecular basis of the more common form of the disease (type I), characterized by quantitative C1-Inhibitor deficiencies. Results obtained in several laboratories can be interpreted in the light of the restriction maps and of the exon-intron structure of the normal C1-Inhibitor gene that have been published recently. Several partial deletions of either exon 4 or exon 7 or of larger portions of the 5' end of the gene and a duplication of exon 4 have been described. These gene alterations are essentially family-specific and they account for at least fifteen-percent of the defects in type I hereditary angioedema. Detailed sequences analyses of cloned defective genes indicate that clusters of repetitive sequences of the Alu family, located within several introns, are responsible for the relatively high frequency of gross gene alterations observed at the C1-Inhibitor locus. In contrast, most of the defects that lead to production of dysfunctional proteins appear to be point mutations within the P1 residue of the reactive site, whose codon features a hypermutable CpG dinucleotide.

Engineering subtilisin BPN' for site-specific proteolysis

A combination of protein engineering and substrate optimization was used to create variants of the serine protease, subtilisin BPN', which efficiently and specifically cleave a designed target sequence in a fusion protein. The broad substrate specificity of wild-type subtilisin BPN' is greatly restricted by substitution of the catalytic histidine-containing of the catalytic histidine 64 with alanine (H64A) so that certain histidine-containing substrates are preferentially hydrolysed (Carter, P., Wells, J.A. Science 237:394-399, 1987). The catalytic efficiency, (kcat/Km), of this H64A variant was increased almost 20-fold by judicious choice of substrate and by installing three additional mutations which increase the activity of wild-type subtilisin. The most favorable substrate sequence identified was introduced as a linker in a fusion protein between a synthetic IgG binding domain of Staphylococcus aureus protein A and Escherichia coli alkaline phosphatase. The fusion protein (affinity purified on an IgG column) was cleaved by the prototype H64A enzyme and its improved variant, efficiently and exclusively at the target site, to liberate an alkaline phosphatase product of the expected size and N-terminal sequence. Several features of H64A variants of subtilisin make them attractive for site-specific proteolysis of fusion proteins: they have exquisite substrate specificity on the N-terminal side of the cleavage site and yet are broadly specific on the C-terminal side; they can be produced in large quantities and remain highly active even in the presence of detergents, reductants (modest concentrations), protease inhibitors, at high temperatures, or when specifically immobilized on a solid support.

Dissecting the catalytic triad of a serine protease

Serine proteases are present in virtually all organisms and function both inside and outside the cell; they exist as two families, the 'trypsin-like' and the 'subtilisin-like', that have independently evolved a similar catalytic device characterized by the Ser, His, Asp triad, an oxyanion binding site, and possibly other determinants that stabilize the transition state (Fig. 1). For Bacillus amyloliquefaciens subtilisin, these functional elements impart a total rate enhancement of at least 10(9) to 10(10) times the non-enzymatic hydrolysis of amide bonds. We have examined the catalytic importance and interplay between residues within the catalytic triad by individual or multiple replacement with alanine(s), using site-directed mutagenesis of the cloned B. amyloliquefaciens subtilisin gene. Alanine substitutions were chosen to minimize unfavourable steric contacts and to avoid imposing new charge interactions or hydrogen bonds from the substituted side chains. In contrast to the effect of mutations in residues involved in substrate binding, the mutations in the catalytic triad greatly reduce the turnover number and cause only minor effects on the Michaelis constant. Kinetic analyses of the multiple mutants demonstrate that the residues within the triad interact synergistically to accelerate amide bond hydrolysis by a factor of approximately 2 X 10(6).

Renal brush border glutamine transport: comparison between in situ and isolate membrane vesicle uptake

Glutamine uptake by renal cortical brush-border vesicles was compared to transport expressed by the functioning isolated kidney. Comparisons were made with regard to sodium dependency and the adaptive increase induced by chronic metabolic acidosis in the rat. The results show an absolute dependency upon a sodium gradient; sodium-independent glutamine uptake has no counterpart in situ. In addition, acidosis-induced adaptive increase in vesicle glutamine uptake has no counterpart in situ. Rather, the apparent adaptation reflects extravesicular gamma-glutamyltransferase-mediated conversion to glutamate and subsequent accumulation; acidosis-induced adaptation of this enzyme largely explains the apparent adaptation in glutamine uptake. Consequently the role of membrane transport in glutamine flux regulation can be assessed providing metabolic conversion is controlled.

Axillary versus rectal temperatures in preterm infants under radiant warmers

Twenty-five preterm neonates were studied to determine whether monitoring of body temperature may be accomplished by taking axillary instead of rectal temperatures. Both axillary and rectal temperatures were taken simultaneously 12 times over a two-day period. Temperatures were recorded at three, five, eight, and ten minutes. The researchers concluded that an axillary measurement of temperature may be adequately substituted for rectal measurement of temperature.

Engineering enzyme specificity by "substrate-assisted catalysis"

A novel approach to engineering enzyme specificity is presented in which a catalytic group from an enzyme is first removed by site-directed mutagenesis causing inactivation. Activity is then partially restored by substrates containing the missing catalytic functional group. Replacement of the catalytic His with Ala in the Bacillus amyloliquefaciens subtilisin gene (the mutant is designated His64Ala) by site-directed mutagenesis reduces the catalytic efficiency (kcat/Km) by a factor of a million when assayed with N-succinyl-L-Phe-L-Ala-L-Ala-L-Phe-p-nitroanilide (sFAAF-pNA). Model building studies showed that a His side chain at the P2 position of a substrate bound at the active site of subtilisin could be virtually superimposed on the catalytic His side chain of this serine protease. Accordingly, the His64Ala mutant hydrolyzes a His P2 substrate (sFAHF-pNA) up to 400 times faster than a homologous Ala P2 or Gln P2 substrate (sFAAF-pNA or sFAQF-pNA) at pH 8.0. In contrast, the wild-type enzyme hydrolyzes these three substrates with similar catalytic efficiencies. Additional data from substrate-dependent pH profiles and hydrolysis of large polypeptides indicate that the His64Ala mutant enzyme can recover partially the function of the lost catalytic histidine from a His P2 side chain on the substrate. Such "substrate-assisted catalysis" provides a new basis for engineering enzymes with very narrow and potentially useful substrate specificities. These studies also suggest a possible functional intermediate in the evolution of the catalytic triad of serine proteases.

Site-directed mutagenesis

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Construction of heterodimer tyrosyl-tRNA synthetase shows tRNATyr interacts with both subunits

The tyrosyl-tRNA synthetase (EC 6.1.1.1) from Bacillus stearothermophilus is a dimer of two identical subunits. The dimer shows "half-of-the-sites" reactivity in that only one molecule of tyrosyladenylate is formed and one molecule of tRNATyr binds per dimer. To identify whether the tRNATyr binds to a single subunit in the dimer, or to both subunits, heterodimers were constructed by mixing two variant dimers together in 8 M urea. As the unfolded protein is electrophoresed into a native polyacrylamide gel, it refolds and reassociates, and heterodimers can be purified from the parental dimers. Kinetic analysis of heterodimers formed between variant enzymes with defective tyrosine activation or tRNA aminoacylation shows that a molecule of tRNATyr interacts with the N-terminal region of one subunit and the C-terminal region of the other subunit in the dimer.

Fine structure-activity analysis of mutations at position 51 of tyrosyl-tRNA synthetase

Residue Thr-51 at the active site of tyrosyl-tRNA synthetase (Bacillus stearothermophilus) has been replaced with all the smaller amino acids by protein engineering to investigate direct and indirect effects of mutation on substrate binding and catalysis. The gamma-hydroxyl group of Thr-51 was thought to be 0.5 A too far from the ribose ring oxygen of ATP to form a hydrogen bond. Consistent with this, it is found that mutation of Thr-51----Cys-51, which should place the gamma-thiol group within its correct distance for hydrogen bonding, increases the affinity of the enzyme for ATP. Other mutations (Ser-51, Ala-51, and Gly-51) show the contributions to binding of the other atoms in the side chain of Thr-51. A family of enzymes has been produced, TyrTS(Thr-51) (wild type), TyrTS(Ala-51), TyrTS(Cys-51), and TyrTS(Pro-51), in which the value of kcat/KM for ATP in aminoacylation increases along the series. This is achieved by the value of KM decreasing significantly (2.5, 1.25, 0.29, and 0.019 mM, respectively) while there are smaller decreases in kcat (4.7, 4.0, 2.9, and 1.8 s-1, respectively). These variations cause each one of the enzymes to be more active than the others at particular concentrations of ATP. For example, at concentrations of ATP greater than 5.9 mM, TyrTS(Thr-51) is the most active, while TyrTS(Ala-51), TyrTS(Cys-51), and TyrTS(Pro-51) are the most active at 5.9-2.2, 2.2-0.42, and less than 0.42 mM ATP, respectively. Interestingly, position 51 shows variation in tyrosyl-tRNA synthetases isolated from different organisms.

Probing histidine-substrate interactions in tyrosyl-tRNA synthetase using asparagine and glutamine replacements

We have analyzed the interactions of a histidine residue with a substrate using site-directed mutagenesis. Previous studies on tyrosyl-tRNA synthetase from Bacillus stearothermophilus have shown that a histidine residue (His-48) makes an interaction with ATP, which is improved on mutating Thr-51----Pro-51. We find on replacing His-48 in wild-type enzyme with either asparagine or glutamine that Asn-48 is equally as good as His-48 but His-48----Gln-48 leads to a far lower activity. The side chain of an asparagine residue may be superimposed on that of a histidine so that the amide-NH2 group of asparagine occupies the same position as the pi-N of histidine, whereas the equivalent -NH2 group of glutamine may be superimposed upon the tau-N. This suggests that it is the pi-N of histidine that hydrogen bonds with ATP and that there is no significant electrostatic interaction between the histidine and ATP. Incorporating the Pro-51 mutation into each of the Asn-48 and Gln-48 mutants gives an improvement in the affinity of the enzyme for ATP, but this improvement is less than that seen with the wild-type enzyme.

Engineering of tyrosyl tRNA synthetase

The gene encoding the enzyme tyrosyl tRNA synthetase from Bacillus stearothermophilus has been systematically altered using synthetic oligonucleotides as mutagens. The construction of mutations has been facilitated by using strains of bacteria defective in mismatch repair and also by utilising a genetic marker in the M13 strain (such as an amber mutation, or an EcoK or EcoB site) which allows selection for the progeny of M13 replication derived from the minus (mutagenized) strand. Several mutations have been constructed in the ATP binding site to elucidate the roles of individual residues in catalysis and substrate binding and it has even been possible to construct mutants which have improved affinity for ATP. Mutations in various surface lysine and arginine residues have allowed us to identify potential contacts with the tRNA, and indicate that a cluster of basic residues close to the C-terminus of the enzyme probably makes important interactions with the tRNA.

Improved oligonucleotide site-directed mutagenesis using M13 vectors

An improved method is described for the construction of mutations in M13 vectors using synthetic oligonucleotides. The DNA is first cloned into a novel M13 vector (based upon M13mp18 or M13mp19), which carries a genetic marker that can be selected against, such as an EcoK or EcoB site, or an amber mutation in an essential phage gene. In this "coupled priming" technique, one primer is used to construct the silent mutation of interest, and a second primer is used to eliminate the selectable marker on the minus strand. After primer extension and ligation, the heteroduplex DNA is transfected into a strain of E. coli which is repair deficient and selects against the plus strand marker. Over 50 mutants have been constructed with this approach, and the yields can be excellent (up to 70%). For the stepwise construction of mutations using separate rounds of mutagenesis, the EcoK and EcoB markers offer a particular advantage over the amber marker. They permit selection in each round, as it is possible to cycle between the two markers. However for construction of multiple mutations over a short region, long synthetic oligonucleotides with multiple mismatches to the template can offer an alternative strategy.

Renal abnormalities and spondylometaphyseal dysplasia

A renal lesion has not been previously described in association with spondylometaphyseal dysplasia. A case of nephrotic syndrome with progression to renal failure from focal segmental glomerulosclerosis is described.

Hydrogen bonding and biological specificity analysed by protein engineering

The role of complementary hydrogen bonding as a determinant of biological specificity has been examined by protein engineering of the tyrosyl-tRNA synthetase. Deletion of a side chain between enzyme and substrate to leave an unpaired, uncharged hydrogen-bond donor or acceptor weakens binding energy by only 0.5-1.5 kcal mol-1. But the presence of an unpaired and charged donor or acceptor weakens binding by a further approximately 3 kcal mol-1.

A large increase in enzyme-substrate affinity by protein engineering

A single point mutation has been engineered in the tyrosyl-tRNA synthetase that improves its affinity (KM) for its substrate ATP by a factor of 100. In the crystal structure of the tyrosyl tRNA synthetase (of Bacillus stearothermophilus), the side-chain hydroxyl of Thr 51 appears to make a weak hydrogen bond with the AMP moiety of the substrate intermediate, tyrosyl adenylate. In the absence of substrate, however, the hydroxyl group should make a strong hydrogen bond with water which would favour dissociation of the enzyme-substrate complex. We have used oligodeoxynucleotide-directed mutagenesis to construct two point mutants at this site: one to remove the hydroxyl group (Thr 51 leads to Ala 51) and the other, in addition, to distort the local polypeptide backbone (Thr 51 leads to Pro 51). We report here that both mutants have increased activity (kcat/KM for ATP) but one mutant (Pro 51) shows a massive 25-fold increase due mainly to a lowered KM for ATP. This demonstrates dramatically the potential of in vitro mutagenesis for improving the affinity of an enzyme for its substrate.

Algorithms for processing spatial information

Pairs of stimuli taken from a psychometric measure of spatial aptitude were shown to 9-year-olds, 13-year-olds, and adults. The stimuli in pairs were (a) either identical or mirror images, and (b) presented in orientations that differed by 0-150 degrees. Individuals judged, as rapidly as possible, if the stimuli in a pair would be identical or mirror images if presented at the same orientation. In Experiment 1, in which the stimuli were letter-like characters, at all ages most persons solved the problems using an algorithm in which an individual encodes the stimuli in working memory, mentally rotates one stimulus to the orientation of the other, compares them to determine if they are identical, and responds. In Experiment 2, the stimuli were multielement flags; here, the modal algorithm for both 9- and 13-year-olds differed from the previously described algorithm in that if the comparison process revealed that the stimuli were dissimilar, individuals did not respond immediately, but continued processing until a self-imposed deadline was reached. Among adults, the modal algorithm was the same one used in Experiment 1. Results are discussed in terms of the roles of encoding in contributing to the use of a particular algorithm.

Congenital laryngeal hemangioma

Congenital subglottic hemangioma consistently occurs in a site below the vocal cord. It is a distinct clinical entity with typical clinical features. However, congenital hemangioma in other sites can cause airway obstruction. An anatomical classification is proposed on the basis of review of 23 consecutive cases. It is important to accurately identify the site and distribution of the lesion before commencing treatment. Radiation has been an acknowledged form of treatment, and in our hospital we have confirmed that radiation therapy, either by external beam, or by insertion of a radioactive gold grain, gives good results. The theoretical possibility of radiation-induced malignancy in the thyroid gland is reduced to an absolute minimum by use of a radioactive grain for localized tumor-dose with minimum radiation of surrounding tissue.

Ten-year review of pediatric tracheotomy

One hundred sixty-four consecutive tracheotomies are reviewed over the 10-year period 1972-1981. Early in the series acute inflammatory airway obstruction was the major indication for tracheotomy, being 60% of cases in the first 3 years. In the last 3 years this fell to approximately 15%. After 1975 nasotracheal intubation replaced tracheotomy for acute epiglottis. More recently it has become the treatment of choice for acute laryngotracheobronchitis. Tracheotomy prior to reconstructive surgery for major craniofacial abnormalities is becoming more frequent. Acquired subglottic stenosis is not a problem in our hospital despite the use of long-term nasotracheal intubation in premature infants, and no tracheotomies were performed for this indication. There were few major complications. Decannulation difficulties were due to obstruction by stomal granulation tissue or displaced flap of anterior tracheal wall. There was no case of hemorrhage, no posttracheotomy stenosis, and no death was attributable to tracheotomy. These results demonstrate that in a major pediatric hospital tracheotomy is a relatively safe and effective procedure with minimal morbidity.