Identification of a single and non-essential cysteine residue in dextransucrase of Leuconostoc mesenteroides NRRL B-512F

Amino acid analysis of purified dextransucrase (sucrose: 1,6-α-D-glucan 6-α-D-glucosyltransferase EC 2.4.1.5) from Leuconostoc mesenteroides NRRL B-512F was carried out. The enzyme is virtually devoid of cysteine residue there being only one cysteine residue in the whole enzyme molecule comprising over 1500 amino acid residues. The enzyme is rich in acidic amino acid residues. The number of amino acid residues was calculated based on the molecular weight of 188,000 (Goyal and Katiyar 1994). Amino sugars were not found, implying that the enzyme is not a glycoprotein. It has been shown earlier that the cysteine residue in dextransucrase is not essential for enzyme activity (Goyal and Katiyar 1998). The presence of only one cysteine residue per enzyme molecule illustrates that its tertiary structure is solely dependent on other types of non-covalent interactions such as hydrogen bonding, ionic and nonpolar hydrophobic interactions.     

Expression patterns and adaptive functional diversity of vertebrate myoglobins

Recent years have witnessed a new round of research on one of the most studied proteins - myoglobin (Mb), the oxygen (O₂) carrier of skeletal and heart muscle. Two major discoveries have stimulated research in this field: 1) that Mb has additional protecting functions, such as the regulation of in vivo levels of the signaling molecule nitric oxide (NO) by scavenging and generating NO during normoxia and hypoxia, respectively; and 2) that Mb in vertebrates (particularly fish) is expressed as tissue-specific isoforms in other tissues than heart and skeletal muscle, such as vessel endothelium, liver and brain, as found in cyprinid fish. Furthermore, Mb has also been found to protect against oxidative stress after hypoxia and reoxygenation and to undergo allosteric, O₂-linked S-nitrosation, as in rainbow trout. Overall, the emerging evidence, particularly from fish species, indicates that Mb fulfills a broader array of physiological functions in a wider range of different tissues than hitherto appreciated. This new knowledge helps to better understand how variations in Mb structure and function may correlate with differences in animals' lifestyles and hypoxia-tolerance. This review integrates old and new results on Mb expression patterns and functional properties amongst vertebrates and discusses how these may relate to adaptive variations in different species. This article is part of a special issue entitled: Oxygen Binding and Sensing Proteins.     

A CRYGC gene mutation associated with autosomal dominant pulverulent cataract

Purpose

To describe at molecular level a family with pulverulent congenital cataract associated with a CRYGC gene mutation.

Methods

One family with several affected members with pulverulent congenital cataract and 230 healthy controls were examined. Genomic DNA from leukocytes was isolated to analyze the CRYGA-D cluster, CX46, CX50 and MIP genes through high-resolution melting curve and DNA sequencing.

Results

DNA sequencing in the affected members revealed the c.143G>A mutation (p.R48H) in exon 2 of the CRYGC gene; 230 healthy controls and ten healthy relatives were also analyzed and none of them showed the c.143G>A mutation. No other polymorphisms or mutations were found to be present.

Conclusion

In the present study, we described a family with pulverulent congenital cataract that segregated the c.143G>A mutation (p.R48H) in the CRYGC gene. A few mutations have been described in the CRYGC gene in autosomal dominant cataract, none of them with pulverulent cataract making clear the clinical heterogeneity of congenital cataract. This mutation has been associated with the phenotype of congenital cataract but also is considered an SNP in the NCBI data base. Our data and previous report suggest that p.R48H could be a disease-causing mutation and not an SNP.     

Modelling family 2 cystatins and their interaction with papain

Cystatins are extensively studied cysteine protease inhibitors, found in wide range of organisms with highly conserved structural folds. S-type of cystatins is well known for their abundance in saliva, high selectivity and poorer activity towards host cysteine proteases in comparison to their immediate ancestor cystatin C. Despite more than 90% sequence similarity, the members of this group show highly dissimilar binding affinity towards papain. Cystatin M/E is a potent inhibitor of legumain and papain like cysteine proteases and recognized for its involvement in skin barrier formation and potential role as a tumor suppressor gene. However, the structures of these proteins and their complexes with papain or legumain are still unknown. In the present study, we have employed computational methods to get insight into the interactions between papain and cystatins. Three-dimensional structures of the cystatins are generated by homology modelling, refined with molecular dynamics simulation, validated through numerous web servers and finally complexed with papain using ZDOCK algorithm in Discovery Studio. A high degree of shape complementarity is observed within the complexes, stabilized by numerous hydrogen bonds (HB) and hydrophobic interactions. Using interaction energy, HB and solvent accessible surface area analyses, we have identified a series of key residues that may be involved in papain–cystatin interaction. Differential approaches of cystatins towards papain are also noticed which are possibly responsible for diverse inhibitory activity within the group. These findings will improve our understanding of fundamental inhibitory mechanisms of cystatin and provide clues for further research.     

Purification and Characterization of an Extracellular Low Temperature-Active and Alkaline Stable Peptidase from Psychrotrophic Acinetobacter sp. MN 12 MTCC (10786)

An extracellular low temperature-active alkaline stable peptidase from Acinetobacter sp. MN 12 was purified to homogeneity with a purification fold of 9.8. The enzyme exhibited specific activity of 6,540 U/mg protein, with an apparent molecular weight of 35 kDa. The purified enzyme was active over broad range of temperature from 4 to 60 °C with optimum activity at 40 °C. The enzyme retained more than 75 % of activity over a broad range of pH (7.0–11.0) with optimum activity at pH 9.0. The purified peptidase was strongly inhibited by phenylmethylsulfonyl fluoride, giving an indication of serine type. The K _m and V _max for casein and gelatin were 0.3529, 2.03 mg/ml and 294.11, 384.61 μg/ml/min respectively. The peptidase was compatible with surfactants, oxidizing agents and commercial detergents, and effectively removed dried blood stains on cotton fabrics at low temperature ranging from 15 to 35 °C.     

Interaction of dipeptydil peptidase IV with amyloid peptides

The aggregates of amyloid beta peptides (Aβs) are regarded as one of the main pathological hallmarks of Alzheimer’s disease (AD). An imbalance between the rates of synthesis and clearance of Aβs is considered to be a possible cause for the onset of AD. Dipeptidyl peptidases II and IV (DPPII and DPPIV) are serine proteases removing N-terminal dipeptides from polypeptides and proteins with proline or alanine on the penultimate position. Alanine is an N-terminal penultimate residue in Аβs, and we presumed that DPPII and DPPIV could cleave them. The results of present in vitro research demonstrate for the first time the ability of DPPIV to truncate the commercial Aβ40 and Aβ42 peptides, to hinder the fibril formation by them and to participate in the disaggregation of preformed fibrils of these peptides. The increase of absorbance at 334 nm due to complex formation between primary amines with o-phtalaldehyde was used to show cleaving of Aβ40 and Aβ42. The time-dependent increase of the quantity of primary amines during incubation of peptides in the presence of DPPIV suggested their truncation by DPPIV, but not by DPPII. The parameters of the enzymatic breakdown by DPPIV were determined for Aβ40 (K_m = 37.5 μM, k_cat/K_m = 1.7 × 10³ M⁻¹sec⁻¹) and Aβ42 (K_m = 138.4 μM, k_cat/K_m = 1.90 × 10² M⁻¹sec⁻¹). The aggregation-disaggregation of peptides was controlled by visualization on transmission electron microscope and by Thioflavin-T fluorescence on spectrofluorimeter and fluorescent microscope. DPPIV hindered the peptide aggregation/fibrillation during 3-4 days incubation in 20 mM phosphate buffer, pH 7.4, 37 °C by 50–80%. Ovalbumin, BSA and DPPII did not show this effect. In the presence of DPPIV, the preformed fibrils were disaggregated by 30–40%. Conclusion: for the first time it was shown that the Aβ40 and Aβ42 are substrates of DPPIV. DPPIV prohibits the fibrillation of peptides and promotes disaggregation of their preformed aggregates.     

Toward the structure of presenilin/γ-secretase and presenilin homologs

Presenilin is the catalytic component of the γ-secretase complex, a membrane-embedded aspartyl protease that plays a central role in biology and in the pathogenesis of Alzheimer’s disease. Upon assembly with its three protein cofactors (nicastrin, Aph-1 and Pen-2), presenilin undergoes autoproteolysis into two subunits, each of which contributes one of the catalytic aspartates to the active site. A family of presenilin homologs, including signal peptide peptidase, possess proteolytic activity without the need for other protein factors, and these simpler intramembane aspartyl proteases have given insight into the action of presenilin within the γ-secretase complex. Cellular and molecular studies support a nine-transmembrane topology for presenilins and their homologs, and small-molecule inhibitors and cysteine scanning with crosslinking have suggested certain presenilin residues and regions that contribute to substrate recognition and handling. Identification of partial complexes has also offered clues to protein–protein interactions within the γ-secretase complex. Biophysical methods have allowed 3D views of the γ-secretase complex and presenilins. Most recently, the crystal structure of a microbial presenilin homolog has confirmed a nine-transmembrane topology and intramembranous location and proximity of the two conserved and essential aspartates. The crystal structure also provides a platform for the formulation of specific hypotheses regarding substrate interaction and catalysis as well as the pathogenic mechanism of Alzheimer-causing presenilin mutations. This article is part of a Special Issue entitled: Intramembrane Proteases.     

Exclusive rewards in mutualisms: ant proteases and plant protease inhibitors create a lock–key system to protect Acacia food bodies from exploitation

Myrmecophytic Acacia species produce food bodies (FBs) to nourish ants of the Pseudomyrmex ferrugineus group, with which they live in an obligate mutualism. We investigated how the FBs are protected from exploiting nonmutualists. Two‐dimensional gel electrophoresis of the FB proteomes and consecutive protein sequencing indicated the presence of several Kunitz‐type protease inhibitors (PIs). PIs extracted from Acacia FBs were biologically active, as they effectively reduced the trypsin‐like and elastase‐like proteolytic activity in the guts of seed‐feeding beetles (Prostephanus truncatus and Zabrotes subfasciatus), which were used as nonadapted herbivores representing potential exploiters. By contrast, the legitimate mutualistic consumers maintained high proteolytic activity dominated by chymotrypsin 1, which was insensitive to the FB PIs. Larvae of an exploiter ant (Pseudomyrmex gracilis) taken from Acacia hosts exhibited lower overall proteolytic activity than the mutualists. The proteases of this exploiter exhibited mainly elastase‐like and to a lower degree chymotrypsin 1‐like activity. We conclude that the mutualist ants possess specifically those proteases that are least sensitive to the PIs in their specific food source, whereas the congeneric exploiter ant appears partly, but not completely, adapted to consume Acacia FBs. By contrast, any consumption of the FBs by nonadapted exploiters would effectively inhibit their digestive capacities. We suggest that the term ‘exclusive rewards’ can be used to describe situations similar to the one that has evolved in myrmecophytic Acacia species, which reward mutualists with FBs but safeguard the reward from exploitation by generalists by making the FBs difficult for the nonadapted consumer to use.     

Involvement of serotonin transporter extracellular loop 1 in serotonin binding and transport

Residues Tyr-110 through Gly-115 of serotonin transporter were replaced, one at a time, with cysteine. Of these mutants, only G113C retained full activity for transport, Q111C and N112C retained partial activity, but Y110C, G114C and G115C were inactive. Poor surface expression was at least partly responsible for the lack of transport by G114C and G115C. In membrane preparations, Y110C through G113C all bound a high affinity cocaine analog similarly to the wild type. Treatment with methanethiosulfonate reagents increased the transport activity of Q111C and N112C to essentially wild-type levels but had no measurable effect on the other mutants. The decreased activity of Q111C and N112C resulted from an increase in the K_M for serotonin that was not accompanied by a decrease in serotonin binding affinity. Superfusion experiments indicated a defect in 5-HT exchange. Modification of the inserted cysteine residues reversed the increase in K_M and the poor exchange, also with no effect on serotonin affinity. The results suggest that Gln-111 and Asn-112 are not required for substrate binding but participate in subsequent steps in the transport cycle.     

Isolation and Characterization of a Cysteine Protease of Freesia Corms

A protease, freesia protease (FP)-A, was purified to electrophoretic homogeneity from regular freesia (Freesia reflacta) corms in harvest time. The M _r of FP-A was estimated to be 24 k by SDS-PAGE. The optimum pH of the enzyme was 8.0 using a casein substrate. These enzymes were strongly inhibited by p-chloromercuribenzoic acid but not by phenylmethane-sulfonylfluoride and EDTA. These results indicate that FP-A belongs to the cysteine proteases. The amino terminal sequence of FP-A was similar to that of papain, and the sequences was regarded to the conservative residues of cysteine protease. From the hydrolysis of peptidyl-pNAs, the specificity of FP-A was found to be broad. It was thought that FP-A was a new protease from freesia corms.