Purification of a novel serine proteinase inhibitor from the skeletal muscle of white croaker (Argyrosomus argentatus)

Novel N-substituted 5-phosphate-d-arabinonamide derivatives as strong inhibitors of phosphoglucose isomerases: Synthesis, structure-activity relationship and crystallographic studies

Phosphoglucose isomerase (PGI) is a cytosolic enzyme that catalyzes the reversible interconversion of d-glucose 6-phosphate and d-fructose 6-phosphate in glycolysis. Outside the cell, PGI is also known as autocrine motility factor (AMF), a cytokine secreted by a large variety of tumor cells that stimulates motility of cancer cells in vitro and metastases development in vivo. Human PGI and AMF are strictly identical proteins both in terms of sequence and 3D structure, and AMF activity is known to involve, at least in part, the enzymatic active site. Hence, with the purpose of finding new strong AMF-PGI inhibitors that could be potentially used as anticancer agents and/or as bioreceptors for carbohydrate-based electrochemical biosensors, we report in this study the synthesis and kinetic evaluation of several new human PGI inhibitors derived from the synthon 5-phospho-d-arabinono-1,4-lactone. Although not designed as high-energy intermediate analogue inhibitors of the enzyme catalyzed isomerization reaction, several of these N-substituted 5-phosphate-d-arabinonamide derivatives appears as new strong PGI inhibitors. For one of them, we report its crystal structure in complex with human PGI at 2.38 Å. Detailed analysis of its interactions at the active site reveals a new binding mode and shows that human PGI is relatively tolerant for modified inhibitors at the "head" C-1 part, offering promising perspectives for the future design of carbohydrate-based biosensors.

Clinical and Molecular Spectrum of Glucose-6-Phosphate Isomerase Deficiency. Report of 12 New Cases

Glucose-6-phosphate isomerase (GPI, EC 5.3.1.9) is a dimeric enzyme that catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate, the second reaction step of glycolysis. GPI deficiency, transmitted as an autosomal recessive trait, is considered the second most common erythro-enzymopathy of anaerobic glycolysis, after pyruvate kinase deficiency. Despite this, this defect may sometimes be misdiagnosed and only about 60 cases of GPI deficiency have been reported. GPI deficient patients are affected by chronic non-spherocytic hemolytic anemia of variable severity; in rare cases, intellectual disability or neuromuscular symptoms have also been reported. The gene locus encoding GPI is located on chromosome 19q13.1 and contains 18 exons. So far, about 40 causative mutations have been identified. We report the clinical, hematological and molecular characteristics of 12 GPI deficient cases (eight males, four females) from 11 families, with a median age at admission of 13 years (ranging from 1 to 51); eight of them were of Italian origin. Patients displayed moderate to severe anemia, that improves with aging. Splenectomy does not always result in the amelioration of anemia but may be considered in transfusion-dependent patients to reduce transfusion intervals. None of the patients described here displayed neurological impairment attributable to the enzyme defect. We identified 13 different mutations in the GPI gene, six of them have never been described before; the new mutations affect highly conserved residues and were not detected in 1000 Genomes and HGMD databases and were considered pathogenic by several mutation algorithms. This is the largest series of GPI deficient patients so far reported in a single study. The study confirms the great heterogeneity of the molecular defect and provides new insights on clinical and molecular aspects of this disease.

Monoclonal antibodies against autocrine motility factor suppress gastric cancer

Autocrine motility factor (AMF), which is a secreted form of phosphoglucose isomerase, is mainly secreted by various tumors and has cytokine-like activity. AMF is known to stimulate proliferation, survival and metastasis of cancer cells, and angiogenesis within a tumor. The present study investigated whether inhibition of AMF using targeted-antibodies was able to suppress the growth of cancer. A migration assay using a Boyden chamber was utilized to measure the activity of AMF on the motility of cancer cells. A recombinant human AMF (rhAMF) prepared from E. coli transformed with the pET22b-AMF vector increased the motility of MDA-MB-231 and A549 cells, but it did not affect that of NCI-N87 or HepG2 cells, which exhibited the ability to secrete high amounts of their own endogenous AMF into the culture medium. The extent to which the AMF receptor was expressed on cancer cells did not correlate clearly with the cell motility stimulated by rhAMF. In A549-xenografted nude mice treated with sunitinib or cetuximab, a decrease in the plasma AMF concentration was accompanied by a reduction in tumor weight, suggesting an association between the plasma AMF concentration and anticancer activity. A monoclonal antibody (9A-4H), which revealed a high binding affinity for E. coli-derived rhAMF, significantly suppressed the growth of tumors in Balb/c nude mice transplanted with the human gastric cancer cell line NCI-N87, to the similar extent as trastuzumab, an anticancer antibody. The present study suggests, for the first time, that an antibody specific to AMF may be a therapeutic agent for gastric cancer.

Survival of glucose phosphate isomerase null somatic cells and germ cells in adult mouse chimaeras

The mouse Gpi1 gene encodes the glycolytic enzyme glucose phosphate isomerase. Homozygous Gpi1(-/-) null mouse embryos die but a previous study showed that some homozygous Gpi1(-/-) null cells survived when combined with wild-type cells in fetal chimaeras. One adult female Gpi1(-/-)↔Gpi1(c/c) chimaera with functional Gpi1(-/-) null oocytes was also identified in a preliminary study. The aims were to characterise the survival of Gpi1(-/-) null cells in adult Gpi1(-/-)↔Gpi1(c/c) chimaeras and determine if Gpi1(-/-) null germ cells are functional. Analysis of adult Gpi1(-/-)↔Gpi1(c/c) chimaeras with pigment and a reiterated transgenic lineage marker showed that low numbers of homozygous Gpi1(-/-) null cells could survive in many tissues of adult chimaeras, including oocytes. Breeding experiments confirmed that Gpi1(-/-) null oocytes in one female Gpi1(-/-)↔Gpi1(c/c) chimaera were functional and provided preliminary evidence that one male putative Gpi1(-/-)↔Gpi1(c/c) chimaera produced functional spermatozoa from homozygous Gpi1(-/-) null germ cells. Although the male chimaera was almost certainly Gpi1(-/-)↔Gpi1(c/c), this part of the study is considered preliminary because only blood was typed for GPI. Gpi1(-/-) null germ cells should survive in a chimaeric testis if they are supported by wild-type Sertoli cells. It is also feasible that spermatozoa could bypass a block at GPI, but not blocks at some later steps in glycolysis, by using fructose, rather than glucose, as the substrate for glycolysis. Although chimaera analysis proved inefficient for studying the fate of Gpi1(-/-) null germ cells, it successfully identified functional Gpi1(-/-) null oocytes and revealed that some Gpi1(-/-) null cells could survive in many adult tissues.

Increased Expression of the Autocrine Motility Factor is Associated With Poor Prognosis in Patients With Clear Cell-Renal Cell Carcinoma

Glucose-6-phosphate isomerase (GPI), also known as phosphoglucose isomerase, was initially identified as the second glycolytic enzyme that catalyzes the interconversion of glucose-6-phosphate to fructose-6-phosphate. Later studies demonstrated that GPI was the same as the autocrine motility factor (AMF), and that it mediates its biological effects through the interaction with its surface receptor (AMFR/gp78). In this study, we assessed the role of GPI/AMF as a prognostic factor for clear cell renal cell carcinoma (ccRCC) cancer-specific (CSS) and progression-free survival (PFS). In addition, we evaluated the expression and localization of GPI/AMF and AMFR, using tissue microarray-based immunohistochemistry (TMA-IHC), indirect immunofluorescence (IF), and confocal microscopy analysis.Primary renal tumor and nonneoplastic tissues were collected from 180 patients who underwent nephrectomy for ccRCC. TMA-IHC and IF staining showed an increased signal for both GPI and AMFR in cancer cells, and their colocalization on plasma membrane. Kaplan-Meier curves showed significant differences in CSS and PFS among groups of patients with high versus low GPI expression. In particular, patients with high tissue levels of GPI had a 5-year survival rate of 58.8%, as compared to 92.1% for subjects with low levels (P < 0.0001). Similar findings were observed for PFS (56.8% vs 93.3% at 5 years). At multivariate analysis, GPI was an independent adverse prognostic factor for CSS (HR = 1.26; P = 0.001), and PFS (HR = 1.16; P = 0.01).In conclusion, our data suggest that GPI could serve as a marker of ccRCC aggressiveness and a prognostic factor for CSS and PFS.

AMF/PGI-mediated tumorigenesis through MAPK-ERK signaling in endometrial carcinoma

Autocrine motility factor (AMF), which is also known as phosphoglucose isomerase (PGI), enhances tumor cell growth and motility. In this study, we found that AMF and its receptor were both highly expressed in Endometrial Carcinoma (EC) tissues compared to normal tissues. Levels of AMF were increased in serum of endometrial cancer patients. Downregulation of AMF by shRNA inhibited invasion, migration and proliferation as well as growth in a three-dimensional culture. AMF cytokine function, but not enzymatic activity of PGI, regulated tumorigenic activities of AMF. The MAPK-ERK1/2 pathway contributed to AMF-induced effects in EC cells. In agreement, Mek inhibitor decreased AMF-induced invasion, migration and proliferation of EC cells. In addition, in two mouse tumor metastasis models (EC cells delivered through left ventricle or intraperitoneally) AMF-silenced EC cells showed decreased tumor proliferative and metastatic capacities. We suggest that AMF/PGI is a potential therapeutic target in endometrial carcinoma.

Down-regulation of phosphoglucose isomerase/autocrine motility factor enhances gensenoside Rh2 pharmacological action on leukemia KG1α cells

AIMS AND BACKGROUND

Ginsenoside Rh2, which exerts the potent anticancer action both in vitro and in vivo, is one of the most well characterized ginsenosides extracted from ginseng. Although its effects on cancer are significant, the underlying mechanisms remain unknown. In this study, we sought to elucidate possible links between ginsenoside Rh2 and phosphoglucose isomerase/autocrine motility factor (PGI/AMF).

METHODS

KG1α, a leukemia cell line highly expressing PGI/AMF was assessed by western blot analysis and reverse transcription- PCR (RT-PCR) assay after transfection of a small interfering (si)-RNA to silence PGI/AMF. The effect of PGI/ AMF on proliferation was measured by typan blue assay and antibody array. A cell counting kit (CCK)-8 and flow cytometry (FCM) were adopted to investigate the effects of Rh2 on PGI/AMF. The relationships between PGI/AMF and Rh2 associated with Akt, mTOR, Raptor, Rag were detected by western blot analysis.

RESULTS

KG1α cells expressed PGI/AMF and its down-regulation significantly inhibited proliferation. The antibody array indicated that the probable mechanism was reduced expression of PARP, State1, SAPK/JNK and Erk1/2, while those of PRAS40 and p38 were up-regulated. Silencing of PGI/AMF enhanced the sensibility of KG1α to Rh2 by suppressing the expression of mTOR, Raptor and Akt.

CONCLUSION

These results suggested that ginsenoside Rh2 suppressed the proliferation of KG1α, the same as down-regulation of PGI/AMF. Down-regulation of PGI/ AMF enhanced the pharmacological effects of ginsenoside Rh2 on KG1α by reducing Akt/mTOR signaling.

Phosphoglucose isomerase/autocrine motility factor mediates epithelial-mesenchymal transition regulated by miR-200 in breast cancer cells

Phosphoglucose isomerase/autocrine motility factor (PGI/AMF) plays an important role in glycolysis and gluconeogenesis and is associated with invasion and metastasis of cancer cells. We have previously shown its role in the induction of epithelial-mesenchymal transition (EMT) in breast cancer cells, which led to increased aggressiveness; however, the molecular mechanism by which PGI/AMF regulates EMT is not known. Here we show, for the first time, that PGI/AMF overexpression led to an increase in the DNA-binding activity of NF-κB, which, in turn, led to increased expression of ZEB1/ZEB2. The microRNA-200s (miR-200s) miR-200a, miR-200b, and miR-200c are known to negatively regulate the expression of ZEB1/ZEB2, and we found that the expression of miR-200s was lost in PGI/AMF overexpressing MCF-10A cells and in highly invasive MDA-MB-231 cells, which was consistent with increased expression of ZEB1/ZEB2. Moreover, silencing of PGI/AMF expression in MDA-MB-231 cells led to overexpression of miR-200s, which was associated with reversal of EMT phenotype (i.e., mesenchymal-epithelial transition), and these findings were consistent with alterations in the relative expression of epithelial (E-cadherin) and mesenchymal (vimentin, ZEB1, ZEB2) markers and decreased aggressiveness as judged by clonogenic, motility, and invasion assays. Moreover, either reexpression of miR-200 or silencing of PGI/AMF suppressed pulmonary metastases of MDA-MB-231 cells in vivo, and anti-miR-200 treatment in vivo resulted in increased metastases. Collectively, these results suggest a role of miR-200s in PGI/AMF-induced EMT and thus approaches for upregulation of miR-200s could be a novel therapeutic strategy for the treatment of highly invasive breast cancer.

Mung bean trypsin inhibitor is effective in suppressing the degradation of myofibrillar proteins in the skeletal muscle of blue scad (Decapterus maruadsi)

Mung bean trypsin inhibitor (MBTI) of the Bowman-Birk family was purified to homogeneity with a molecular mass of approximately 9 kDa on tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 8887.25 Da as determined by matrix-assisted laser desorption/ionization-quadrupole ion trap-time-of-flight mass spectrometry (MALDI-QIT-TOF MS). Using blue scad myofibrillar proteins as targets, it was found that, in the absence of MBTI, proteolysis of myofibrillar proteins, especially myosin heavy chain (MHC), could be identified after incubation at 55 °C for 2 h, while in the presence of MBTI, with a final concentration of 25 ng/mL, proteolysis of these proteins was greatly suppressed even after incubation for 3 h. Although cysteine proteinase inhibitor E-64 was also effective in preventing protein degradation, inhibitors for metallo- and asparatic proteinases did not reveal obvious inhibitory effects. Our present results strongly suggested that the naturally occurring legume bean seed protein MBTI can be used as an effective additive in preventing marine fish blue scad surimi gel softening, which is quite possibly caused by myofibril-bound serine proteinase (MBSP).

Diagnostic value of glucose-6-phosphate isomerase in rheumatoid arthritis

BACKGROUND

Although glucose-6-phosphate isomerase (G6PI), anti-G6PI antibodies and G6PI-containing immune complexes (G6PI-CIC) have proved high expression in patients with rheumatoid arthritis (RA), comprehensive evaluation of the G6PI-derived markers, G6PI antigen, anti-G6PI Abs, G6PI-CIC and G6PI mRNA, in the diagnosis of RA remains necessary.

METHODS

We measured G6PI antigen, anti-G6PI Abs, C1q/G6PI-CIC as well as anti-cyclic citrullinated peptide antibodies (anti-CCP Abs) in serum and concomitantly synovial fluid (SF) by ELISA in RA, other rheumatic diseases and healthy controls. The G6PI mRNA expression in peripheral blood mononuclear cells (PBMCs) was assessed with real-time PCR.

RESULTS

As compared with non-RA patients, RA patients had increased levels of G6PI antigen, anti-G6PI Abs, C1q/G6PI-CIC and G6PI mRNA expression in sera or PBMCs, and increased levels of G6PI and C1q/G6PI-CIC in SF. The serum G6PI levels in RA patients positively correlated with anti-G6PI Abs, C1q/G6PI-CIC, G6PI mRNA, anti-CCP Abs, RF, CRP and ESR, respectively. The area under curve analyses demonstrated that serum G6PI had the best discriminating power for RA and active RA followed by C1q/G6PI-CIC, anti-G6PI Abs and G6PI mRNA. The simultaneous use of serum G6PI and anti-CCP Abs assays in the form of either of them tested positive gave improved sensitivities of 88.1% for RA and 95.8% for active RA.

CONCLUSIONS

Despite the elevated expression of all G6PI-derived markers in RA, the serum G6PI has the best discriminating power among the four G6PI-derived markers. The serum G6PI determination either alone or in combination with anti-CCP Abs improves the diagnosis of RA.

Elevated serum glucose-6-phosphate isomerase correlates with histological disease activity and clinical improvement after initiation of therapy in patients with rheumatoid arthritis

OBJECTIVE

To determine serum glucose-6-phosphate isomerase (GPI) concentrations in patients with rheumatoid arthritis (RA), and to test whether they correlate with objective measures of disease activity.

METHODS

Sera from 116 patients with RA, 69 patients with non-RA rheumatic diseases, and 101 healthy controls were analyzed. Levels of soluble serum GPI were measured by ELISA. Histological disease activity was determined with the synovitis score in synovial needle biopsies from 58 of the 116 patients with RA. Thirty-one of the 58 synovium samples were stained for CD68, CD3, CD20, CD38, CD79a, and CD34 by immunohistochemistry. Demographic data were collected, as well as serological and clinical variables that indicate RA disease activity, for Spearman correlation analysis.

RESULTS

Serum GPI level correlated positively with the synovitis score (r = 0.278, p = 0.034). Significantly higher soluble GPI levels were detected in the RA sera compared with sera from healthy controls and the non-RA disease controls (2.25 ± 2.82 vs 0.03 ± 0.05 and 0.19 ± 0.57 μg/ml, respectively; p < 0.0001). The rate of serum GPI positivity was significantly higher in the RA patients than in the non-RA disease controls (64.7% vs 10.1%; p < 0.0001). Spearman analysis showed no significant correlation between serum GPI level and Disease Activity Score in 28 joints at baseline. After initiation of antirheumatic treatments, GPI levels decreased significantly (2.81 ± 3.12 vs 1.44 ± 2.09 μg/ml; p = 0.016), paralleling improvement of the disease activity indices.

CONCLUSION

Elevated serum GPI may be involved in the synovitis of RA and may prove useful as a serum marker for disease activity of RA.

Structural studies of phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv

Phosphoglucose isomerase (PGI) plays a key role in both glycolysis and gluconeogenesis inside the cell, whereas outside the cell it exhibits cytokine properties. PGI is also known to act as an autocrine motility factor, a neuroleukin agent and a differentiation and maturation mediator. Here, the first crystal structure of PGI from Mycobacterium tuberculosis H37Rv (Mtb) is reported. The structure was refined at 2.25 A resolution and revealed the presence of one molecule in the asymmetric unit with two globular domains. As known previously, the active site of Mtb PGI contains conserved residues including Glu356, Glu216 and His387 (where His387 is from the neighbouring molecule). The crystal structure of Mtb PGI was observed to be rather more similar to human PGI than other nonbacterial PGIs, with only a few differences being detected in the loops, arm and hook regions of the human and Mtb PGIs, suggesting that the M. tuberculosis enzyme uses the same enzyme mechanism.

Crystallization and preliminary X-ray crystallographic study of phosphoglucose isomerase from Plasmodium falciparum

Phosphoglucose isomerase (PGI) is a key enzyme in glycolysis and glycogenesis that catalyses the interconversion of glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P). For crystallographic studies, PGI from the human malaria parasite Plasmodium falciparum (PfPGI) was overproduced in Escherichia coli, purified and crystallized using the hanging-drop vapour-diffusion method. X-ray diffraction data to 1.5 A resolution were collected from an orthorhombic crystal form belonging to space group P2(1)2(1)2(1) with unit-cell parameters a = 103.3, b = 104.1, c = 114.6 A. Structural analysis by molecular replacement is in progress.

Proteinase inhibitory activity of sarcoplasmic proteins from threadfin bream (Nemipterus spp.)

BACKGROUND

Thailand is the second largest surimi producer in the world and 50% of surimi is produced from threadfin bream. During surimi processing, sarcoplasmic proteins are removed through water washing and discarded in the waste stream. This study was aimed at investigating the proteinase inhibitory activity of sarcoplasmic proteins.

RESULTS

Sarcoplasmic proteins from threadfin bream (TBSP) exhibited inhibitory activity toward trypsin but did not inhibit papain and chymotrypsin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis under non-reducing condition stained by trypsin inhibitory activity revealed three protein bands of molecular mass of 95, 41 and 37 kDa. Inhibitory activity of TBSP reached a maximum when subjected to 45 degrees C and completely disappeared at 60 degrees C. The breaking force and deformation of lizardfish surimi gel with added TBSP and pre-incubated at 37 degrees for 20 min increased with additional levels of TBSP (P < 0.05). Trichloroacetic acid-oligopeptide content of lizardfish surimi gel with added TBSP decreased with the addition of 4 g kg(-1) TBSP (P < 0.05). Retention of myosin heavy chain (MHC) increased when TBSP concentration was increased. TBSP effectively protected MHC from proteolysis at 37 degrees C to a similar extent as egg white powder, but efficacy of TBSP was not observed at 65 degrees C.

CONCLUSION

TBSP could be applied to reduce proteolytic degradation of lizardfish surimi or other surimi associated with trypsin-like proteinase, rendering an improvement in surimi gelation set at 37-40 degrees C.

Glucose-6-phosphate isomerase is an endogenous inhibitor to myofibril-bound serine proteinase of crucian carp (Carassius auratus)

Glucose-6-phosphate isomerase (GPI) was purified to homogeneity from the skeletal muscle of crucian carp ( Carassius auratus ) by ammonium sulfate fractionation, column chromatographies of Q-Sepharose, SP-Sepharose, and Superdex 200 with a yield of 8.0%, and purification folds of 468. The molecular mass of GPI was 120 kDa as estimated by gel filtration, while on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two subunits (55 and 65 kDa) were identified, suggesting that it is a heterodimer. Interestingly, GPI revealed specific inhibitory activity toward a myofibril-bound serine proteinase (MBSP) from crucian carp, while no inhibitory activity was identified toward other serine proteinases, such as white croaker MBSP and crucian carp trypsin. Kinetic analysis showed that GPI is a competitive inhibitor toward MBSP, and the K(i) was 0.32 microM. Our present results indicated that the multifunctional protein GPI is an endogenous inhibitor to MBSP and may play a significant role in the regulation of muscular protein metabolism in vivo.

Phosphoglucose isomerase/autocrine motility factor mediates epithelial and mesenchymal phenotype conversions in breast cancer

Phosphoglucose isomerase/autocrine motility factor (PGI/AMF) is a housekeeping gene product/cytokine that catalyzes a step in glycolysis and gluconeogenesis, and acts as a multifunctional cytokine associated with aggressive tumors. PGI/AMF has been correlated significantly with breast cancer progression and poor prognosis in breast cancer. We show here that ectopic expression of PGI/AMF induced epithelial-to-mesenchymal transition (EMT) in MCF10A normal human breast epithelial cells, and inhibition of PGI/AMF expression triggered mesenchymal-to-epithelial transition (MET) in aggressive mesenchymal-type human breast cancer MDA-MB-231 cells. EMT in MCF10A cells was shown by morphologic changes and loss of E-cadherin/beta-catenin-mediated cell-cell adhesion, which is concomitant with the induction of the E-cadherin transcriptional repressor Snail and proteosome-dependent degradation of beta-catenin protein. Molecular analysis showed that PGI/AMF suppressed epithelial marker expressions and enhanced mesenchymal marker expressions. Silencing of PGI/AMF expression by RNA interference in MDA-MB-231 cells induced the reverse processes of EMT including altered cell shape, gain of epithelial marker, and reduction of mesenchymal marker, e.g., MET. Taken together, the results show the involvement of PGI/AMF in both EMT and MET: overexpression of PGI/AMF induces EMT in normal breast epithelial cells and reduction of PGI/AMF expression led to MET in aggressive breast cancer cells. These results suggest for the first time that PGI/AMF is a key gene to both EMT in the initiating step of cancer metastasis and MET in the later stage of metastasis during breast cancer progression.

The complex biology of autocrine motility factor/phosphoglucose isomerase (AMF/PGI) and its receptor, the gp78/AMFR E3 ubiquitin ligase

Phosphoglucose isomerase (PGI) is a glycolytic enzyme that exhibits a dual function as an extracellular cytokine, under the name autocrine motility factor (AMF). Its cell surface receptor, gp78/AMFR, is also localized to the endoplasmic reticulum where it functions as an E3 ubiquitin ligase. Expression of both AMF/PGI and gp78/AMFR is associated with cancer and, in this review, we will discuss various aspects of the biology of this ligand-receptor complex and its role in tumor progression.

The role of autocrine motility factor in tumor and tumor microenvironment

Autocrine motility factor (AMF) is a tumor-secreted cytokine and is abundant at tumor sites, where it may affect the process of tumor growth and metastasis. AMF is a multifunctional protein capable of affecting cell migration, invasion, proliferation, and survival, and possesses phosphoglucose isomerase activity and can catalyze the step in glycolysis and gluconeogenesis. Here, we review the role of AMF and tumor environment on malignant processes. The outcome of metastasis depends on multiple interactions between tumor cells and homeostatic mechanisms, therefore elucidation of the tumor/host interactions in the tumor microenvironment is essential in the development of new prevention and treatment strategies. Such knowledge might provide clues to develop new future therapeutic approaches for human cancers.

Regulation of phosphoglucose isomerase/autocrine motility factor activities by the poly(ADP-ribose) polymerase family-14

Phosphoglucose isomerase (PGI; EC 5.3.1.9) is a ubiquitous cytosolic enzyme essential for glycolysis and gluconeogenesis. PGI is a multifunctional dimeric protein that extracellularly acts as a cytokine [autocrine motility factor (AMF)] eliciting mitogenic, motogenic, and differentiation functions through binding to its cell surface receptor gp78/AMF receptor (AMFR). AMFR contains a seven-transmembrane domain with RING-H2 and leucine zipper motifs showing ubiquitin protein ligase (E3) activity and is exposed on the endoplasmic reticulum surface. Augmented expressions of both PGI/AMF and AMFR have been implicated in tumor progression and metastasis, and an intracellular binding partner of PGI/AMF is expected to regulate in part its diverse biological functions. Thus, we screened a cDNA library using a yeast two-hybrid system to search for interacting protein(s) and report on the finding of poly(ADP-ribose) polymerase-14 (PARP-14) to be a binding partner with PGI/AMF. PARP-14-PGI/AMF interaction was confirmed by coimmunoprecipitation and immunolocalization. We also report that PGI/AMF degradation is mainly regulated by the ubiquitin-lysosome system and RNA interference experiments revealed that PARP-14 inhibits PGI/AMF ubiquitination, thus contributing to its stabilization and secretion. This newly characterized PARP-14 protein should assist in understanding the regulation of PGI/AMF intracellular function(s) and may provide a new therapeutic target for inhibition of PGI/AMF inducing tumor cell migration and invasion during metastasis.

Down-regulation of phosphoglucose isomerase/autocrine motility factor expression sensitizes human fibrosarcoma cells to oxidative stress leading to cellular senescence

Phosphoglucose isomerase/autocrine motility factor (PGI/AMF) is a housekeeping gene product present in all cells, is an essential enzyme of catabolic glycolysis and anabolic gluconeogenesis, and regulates tumor cell growth and metastasis. Because glycolytic enzyme up-regulation of expression contributes to glycolytic flux, leading to increased of cell growth and a resistance to cellular stress of normal fibroblasts whereas down-regulation of PGI/AMF leads to mesenchymal-to-epithelial transition in tumor cells, we examined the involvement of PGI/AMF in overcoming cellular senescence in cancer cells. PGI/AMF cellular expression in HT1080 human fibrosarcoma was down-regulated by small interfering RNA methodology, which resulted in an increased sensitivity to oxidative stress and oxidative stress-induced cellular senescence. Signaling analysis revealed that the senescence pathway involving p21 cyclin-dependent kinase inhibitor was up-regulated in PGI/AMF knockdown cells and that superoxide dismutase is the upstream regulator protein of p21-mediated cellular senescence. A specific inhibitor of PGI/AMF induced cellular senescence and p21 expression in tumor cells exposed to an oxidative stress environment. Taken together, the results presented here suggest that PGI/AMF is involved in oxidative stress-induced cellular senescence and should bring novel insights into the control of cellular growth leading to a new methodology for cancer treatment.

Down-regulation of phosphoglucose isomerase/autocrine motility factor results in mesenchymal-to-epithelial transition of human lung fibrosarcoma cells

Phosphoglucose isomerase (PGI) is one of the glycolytic enzymes and is a multifunctional enzyme that functions in glucose metabolism inside the cell while acting as a cytokine outside the cell, with properties that include autocrine motility factor (AMF) regulating tumor cell motility. Although there are many studies indicating that PGI/AMF has been implicated in progression of metastasis, no direct studies of the significance of exogenous PGI/AMF on tumor progression have been reported. Here, we report on the mesenchymal-to-epithelial transition (MET), which is the reverse phenomenon of the epithelial-to-mesenchymal transition that is associated with loss of cell polarity, loss of epithelia markers, and enhancement of cell motility essential for tumor cell invasion and metastasis. Mesenchymal human fibrosarcoma HT1080 cells, which have naturally high levels of endogenous and exogenous PGI/AMF, were stably transfected with PGI/AMF small interfering RNA (siRNA). The siRNA targeting human PGI/AMF down-regulated the endogenous PGI/AMF expression and completely extinguished the secretion of PGI/AMF in a human fibrosarcoma HT1080, whereas the control siRNA showed no effects. The PGI/AMF siRNA caused cells to change shape dramatically and inhibited cell motility and invasion markedly. Suppression of PGI/AMF led to a contact-dependent inhibition of cell growth. Those PGI/AMF siRNA-transfected cells showed epithelial phenotype. Furthermore, tumor cells with PGI/AMF deficiency lost their abilities to form tumor mass. This study identifies that MET in HT1080 human lung fibrosarcoma cells was initiated by down-regulation of the housekeeping gene product/cytokine PGI/AMF, and the results depicted here suggest a novel therapeutic target/modality for mesenchymal cancers.

Crystallization and preliminary X-ray characterization of phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv

Phosphoglucose isomerase is a ubiquitous enzyme that catalyzes the isomerization of D-glucopyranose-6-phosphate to D-fructofuranose-6-phosphate. The present investigation reports the expression, purification, crystallization and preliminary crystallographic studies of the phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv, which shares 46% sequence identity with that of its human host. The recombinant protein, which was prepared using an Escherichia coli expression system, was crystallized by the hanging-drop vapour-diffusion method. The crystals diffracted to a resolution of 2.8 A and belonged to the orthorhombic space group I2(1)2(1)2(1), with unit-cell parameters a = 109.0, b = 119.8, c = 138.9 A.

Patients with inflammatory arthritic diseases harbor elevated serum and synovial fluid levels of free and immune-complexed glucose-6-phosphate isomerase (G6PI)

In K/BxN mice, anti-glucose-6-phosphate isomerase (G6PI) IgG antibodies (Abs) cause joint-specific inflammation and destruction. Anti-G6PI Abs are also present in humans with inflammatory arthritis, especially among patients with rheumatoid arthritis (RA). A contributing factor to the induction of such autoantibodies may be upregulated expression of the corresponding antigen G6PI in affected tissues and/or increased levels of G6PI in the circulation. To determine G6PI levels and the presence of free G6PI and/or G6PI-containing immune complexes in sera and synovial fluids (SF) of patients with different arthritides, serum and SF obtained concomitantly from 91 clinically well-defined arthritis patients were assessed in a blinded manner for G6PI enzymatic assay and for G6PI protein concentration by ELISA. Sera and SF from patients with immune-based inflammatory arthritis contained significantly higher levels of G6PI enzymatic activity compared to sera or SF from patients with non-immune-based inflammatory arthritis or healthy controls. In addition, significantly higher levels of total G6PI protein concentration (including both enzymatically active and inactive forms) were present in sera of RA patients vs. those with other immune-based or non-immune-based inflammatory arthritis.G6PI in sera and SF were present both as G6PI-containing immune complexes and as free G6PI, with the majority of free G6PI existing as tetramers with lesser amounts of dimers and monomers. Levels of G6PI enzymatic activity in the sera of most immune-based inflammatory arthritis patients are elevated and may reflect ongoing inflammation and cell destruction. The high serum levels of enzymatically inactive forms of G6PI in RA relative to those in other arthritic diseases are partially due to G6PI-containing immune complexes, a portion of which also contains C1q. Overall, our study supports the notion that elevated G6PI levels present in patients with immune-based inflammatory arthritis may contribute to elevated levels of anti-G6PI Abs and G6PI/anti-G6PI immune complexes. This, in turn, may trigger production of proinflammatory cytokines and perpetuate the inflammatory process.

Regulation of phosphoglucose isomerase/autocrine motility factor expression by hypoxia

Phosphoglucose isomerase (PGI; EC 5.3.1.9) is a housekeeping cytosolic enzyme of the sugar metabolism pathways that plays a key role in glycolysis and gluconeogenesis. PGI is a multifunctional dimeric protein that extracellularly acts as a cytokine with properties that include autocrine motility factor (AMF) eliciting mitogenic, motogenic, differentiation functions and has been implicated in tumor progression and metastasis. Since metastasis is regulated in part by hypoxia, which induces the transcription of metastasis-associated genes and anaerobic glycolic metabolism, we questioned whether hypoxia also regulates the expression level of tumor cells' PGI/AMF. We establish here that in the human breast carcinoma BT-549 cells hypoxia enhanced expression of the transcription factor hypoxia-inducible factor (HIF)-1, which in turn led to the up-regulation of PGI/AMF expression and was specifically inhibited by inhibitors of the phosphatidylinositol 3'-kinase signaling pathway. In addition, the hypoxia induction of PGI/AMF expression was suppressed by inhibitors of vascular endothelial growth factor (VEGF) or VEGF receptors, suggesting that hypoxia-inducible VEGF regulates the PGI/AMF expression. Hypoxia also enhanced cancer cell motility, and these effects were strongly inhibited by the PGI/AMF, VEGF, or VEGF receptor inhibitors. The results presented here suggest that under hypoxic conditions the expression of PGI/AMF is regulated in part by the HIF pathway, which in turn increases the flow of the glycolytic cascade leading to an increased anaerobic energy generation; thus, inhibition of PGI/AMF expression and activities may provide a new therapeutic modality for treatment of hypoxic tumors.

Crystal Structures of Mouse Autocrine Motility Factor in Complex with Carbohydrate Phosphate Inhibitors Provide Insight into Structure–Activity Relationship of the Inhibitors

Autocrine motility factor (AMF), a tumor-secreted cytokine, stimulates cell migration in vitro and metastasis in vivo. AMF is identical to the extracellular cytokines neuroleukin and maturation factor and, interestingly, to the intracellular enzyme phosphoglucose isomerase. The cytokine activity of AMF is inhibited by carbohydrate phosphate compounds as they compete for AMF binding with the carbohydrate moiety of the AMF receptor (AMFR), which is a glycosylated seven transmembrane helix protein. Here, we report the first comprehensive high-resolution crystal structure analyses of the inhibitor-free form and the eight types of inhibitor (phosphate, erythrose 4-phosphate (E4P), arabinose 5-phosphate (A5P), sorbitol 6-phosphate (S6P), 6-phosphogluconic acid (6PGA), fructose 6-phosphate (F6P), glucose 6-phosphate (G6P), or mannose 6-phosphate (M6P)) complexes of mouse AMF (mAMF). We assayed the inhibitory activities of these inhibitors against the cytokine activity of mAMF. The inhibitory activities of the six-carbon sugars (G6P, F6P, M6P, and 6PGA) were found to be significantly higher than those of the four or five-carbon sugars (E4P or A5P). The inhibitory activities clearly depend on the length of the inhibitor molecules. A structural comparison revealed that a water-mediated hydrogen bond between one end of the inhibitor and a rigid portion of the protein surface in the shorter-chain inhibitor (E4P) complex is replaced by a direct hydrogen bond in the longer-chain inhibitor (6PGA) complex. Thus, to obtain a new compound with higher inhibitory activities against AMF, water molecules at the inhibitor binding site of AMF should be replaced by a functional group of inhibitors in order to introduce direct interactions with the protein surface. The present structure-activity relationship studies will be valuable not only for designing more effective AMF inhibitors but also for studying general protein-inhibitor interactions.

Further Characterization of a Sarcoplasmic Serine Proteinase from the Skeletal Muscle of White Croaker (Argyrosomus argentatus)

A trypsin-type serine proteinase (WSP) was purified previously from the sarcoplasmic fraction of skeletal muscle of white croaker (Argyrosomus argentatus) by Yanagihara et al. ((1991) Nippon Suisan Gakaishi, 57, 133-142). However, further research on WSP was not carried out. In the present study, we determined the N-terminal amino acid sequence of this enzyme (27 amino acid residues), which revealed relatively high identity in the conserved region to other trypsin-type serine proteinases. Degradation action of WSP on neuropeptides is also reported in this manuscript. The results show that WSP only cleaves at the carboxyl side of Arg or Lys residue of the peptides, especially between dibasic amino acid residues such as Arg-Arg and Arg-Lys.

Glucose phosphate isomerase deficiency: enzymatic and familial characterization of Arg346His mutation

Homozygous glucose phosphate isomerase (GPI) deficiency is one of the most important genetic disorders responsible for chronic non-spherocytic hemolytic anemia (CNSHA), a red blood cell autosomal recessive genetic disorder which causes severe metabolic alterations. In this work, we studied a patient with CNSHA due to an 82% loss of GPI activity resulting from the homozygous missense replacement in cDNA position 1040G>A, which leads to substitution of the protein residue A346H mutation. The enzyme is present in a dimeric form necessary for normal activity; the A346H mutation causes a loss of GPI capability to dimerize, which renders the enzyme more susceptible to thermolability and produces significant changes in erythrocyte metabolism.

Salmon spawning migration and muscle protein metabolism: the August Krogh principle at work

The August Krogh principle, stating that for any particular question in biology, nature holds an ideal study system, was applied by choosing the anorexic, long-distance migration of salmon as a model to analyze protein degradation and amino acid metabolism. Reexamining an original study done over 20 years ago on migrating sockeye salmon (Oncorhynchus nerka), data on fish migration and starvation are reviewed and a general model is developed on how fish deal with muscle proteolysis. It is shown that lysosomal activation and degradation of muscle protein by lysosomal cathepsins, especially cathepsin D and sometimes cathepsin L, are responsible for the degradation of muscle protein during fish migration, maturation and starvation. This strategy is quite the opposite to mammalian muscle wasting, including starvation, uremia, cancer and others, where the ATP-ubiquitin proteasome in conjunction with ancillary systems, constitutes the overwhelming pathway for protein degradation in muscle. In mammals, the lysosome plays a bit part, if any. In contrast, the proteasome plays at best a subordinate role in muscle degradation in piscine systems. This diverging strategy is put into the context of fish metabolism in general, with its high amino acid turnover, reliance on amino acids as oxidative substrates and flux of amino acids from muscle via the liver into gonads during maturation. Brief focus is placed on structure, function and evolution of the key player in fishes: cathepsin D. The gene structure of piscine cathepsin D is outlined, focusing on the existence of duplicate, paralogous, cathepsin D genes in some species and analyzing the relationship between a female and liver-specific aspartyl protease and fish cathepsin Ds. Evolutionary relationships are developed between different groups of piscine cathepsins, aspartyl proteases and other cathepsins. Finally, based on specific changes in muscle enzymes in fish, including migrating salmon, common strategies of amino acid and carbon flux in fish muscle are pointed out, predicting some metabolic concepts that would make ideal application grounds for the August Krogh principle.

Differential Regulation of Phosphoglucose Isomerase/Autocrine Motility Factor Activities by Protein Kinase CK2 Phosphorylation

Phosphoglucose isomerase (PGI; EC 5.3.1.9) is a cytosolic housekeeping enzyme of the sugar metabolism pathways that plays a key role in both glycolysis and gluconeogenesis. PGI is a multifunctional dimeric protein that extracellularly acts as a cytokine with properties that include autocrine motility factor (AMF)-eliciting mitogenic, motogenic, and differentiation functions, and PGI has been implicated in tumor progression and metastasis. Little is known of the biochemical regulation of PGI/AMF activities, although it is known that human PGI/AMF is phosphorylated at Ser(185) by protein kinase CK2 (CK2); however, the physiological significance of this phosphorylation is unknown. Thus, by site-directed mutagenesis, we substituted Ser(185) with aspartic acid (S185D) or glutamic acid (S185E), which introduces a negative charge and conformational changes that mimic phosphorylation. A Ser-to-Ala mutant protein (S185A) was generated to abolish phosphorylation. Biochemical analyses revealed that the phosphorylation mutant proteins of PGI exhibited decreased enzymatic activity, whereas the S185A mutant PGI protein retained full enzymatic activity. PGI phosphorylation by CK2 also led to down-regulation of enzymatic activity. Furthermore, CK2 knockdown by RNA interference was associated with up-regulation of cellular PGI enzymatic activity. The three recombinant mutant proteins exhibited indistinguishable cytokine activity and receptor-binding affinities compared with the wild-type protein. In both in vitro and in vivo assays, the wild-type and S185A mutant proteins underwent active species dimerization, whereas both the S185D and S185E mutant proteins also formed tetramers. These results demonstrate that phosphorylation affects the allosteric kinetic properties of the enzyme, resulting in a less active form of PGI, whereas non-phosphorylated protein species retain cytokine activity. The process by which phosphorylation modulates the enzymatic activity of PGI thus has an important implication for the understanding of the biological regulation of this key glucose metabolism-regulating enzyme.

The enzymatic activity of phosphoglucose isomerase is not required for its cytokine function

PGI is a housekeeping gene encoding phosphoglucose isomerase (PGI) a glycolytic enzyme that also functions as a cytokine (autocrine motility factor (AMF)/neuroleukin/maturation factor) upon secretion from the cell and binding to its 78 kDa seven-transmembrane domain receptor (gp78/AMF-R). PGI contains a CXXC motif, characteristic of redox proteins and possibly evolutionarily related to the CC and CXC motif of the chemokine gene family. Using site-directed mutagenesis, single- and double-deletion (CXC, CC) mutants were created by deleting amino acids 331 and 332 of human PGI, respectively. The mutant proteins lost their enzymatic activity; however, neither of the deletions augmented the proteins' binding affinity to the receptor and all maintained cytokine function. The results demonstrate that the enzymatic activity of PGI is not essential for either receptor binding or cytokine function of human PGI.

Conformational changes in phosphoglucose isomerase induced by ligand binding

Phosphoglucose isomerase (PGI; EC 5.3.1.9) is the second enzyme in glycolysis, where it catalyzes the isomerization of D-glucose-6-phosphate to D-fructose-6-phosphate. It is the same protein as autocrine motility factor, differentiation and maturation mediator, and neuroleukin. Here, we report a new X-ray crystal structure of rabbit PGI (rPGI) without ligands bound in its active site. The structure was solved at 1.8A resolution by isomorphous phasing with a previously solved X-ray crystal structure of the rPGI dimer containing 6-phosphogluconate in its active site. Comparison of the new structure to previously reported structures enables identification of conformational changes that occur during binding of substrate or inhibitor molecules. Ligand binding causes an induced fit of regions containing amino acid residues 209-215, 245-259 and 385-389. This conformational change differs from the change previously reported to occur between the ring-opening and isomerization steps, in which the helix containing residues 513-521 moves toward the bound substrate. Differences between the liganded and unliganded structures are limited to the region within and close to the active-site pocket.

The crystal structure of rabbit phosphoglucose isomerase complexed with 5-phospho-D-arabinonohydroxamic acid

Phosphoglucose isomerase (EC ) catalyzes the second step in glycolysis, the reversible isomerization of D-glucose 6-phosphate to D-fructose 6-phosphate. The reaction mechanism involves acid-base catalysis with proton transfer and proceeds through a cis-enediol(ate) intermediate. 5-Phospho-D-arabinonohydroxamic acid (5PAH) is a synthetic small molecule that resembles the reaction intermediate, differing only in that it has a nitrogen atom in place of C1. Hence, 5PAH is the best inhibitor of the isomerization reaction reported to date with a K(i) of 2 x 10(-7) M. Here we report the crystal structure of rabbit phosphoglucose isomerase complexed with 5PAH at 1.9 A resolution. The interaction of 5PAH with amino acid residues in the enzyme active site supports a model of the catalytic mechanism in which Glu-357 transfers a proton between C1 and C2 and Arg-272 helps stabilize the intermediate. It also suggests a mechanism for proton transfer between O1 and O2.

Phosphoglucose isomerases of hagfish, zebrafish, gray mullet, toad, and snake, with reference to the evolution of the genes in vertebrates

Phosphoglucose isomerase (PGI) is a protein with multiple functions. To infer its structure changes and evolution in vertebrates, we cloned cDNAs encoding PGI genes from hagfish (Paramyxine yangi), gray mullet (Mugil cephalus), zebrafish (Danio rerio), toad (Bufo melanosticus), and snake (Boiga kraepelini). Only one PGI gene was cloned in each of hagfish, toad, and snake, but two PGI genes were found in zebrafish and gray mullet, respectively. The PGI of hagfish encodes 554 amino acids, in contrast to the PGIs of bonyfishes, toad, and snake which encode 553 amino acids and the PGIs of mammals which encode 558 amino acids. Among 558 aligned amino acid sites, there are 314 sites (56.27%) totally conserved. To see if diversifying selection acts on PGI amino acids of vertebrates, we calculated the pairwise ratio of nonsynonymous versus synonymous substitution per site (Ka/Ks) and the ratio of radical amino acid changes versus conservative amino acid changes per sites (dR/dC) between PGI sequences. The average pairwise ratio between nonsynonymous substitutions per nucleotide (Ka) and synonymous substitutions per nucleotide (Ks) among vertebrate PGI sequences equals 0.047 +/- 0.019. The average pairwise ratio between radical amino acid changes and conservative amino acid changes (dR/dC) among the vertebrate PGIs equal 0.938 +/- 0.158 for charge changes, 0.558 +/- 0.085 for polarity changes, and 0.465 +/- 0.0714 when both polarity and volume are considered. There is no amino acid within the vertebrate PGIs under diversifying selection as analyzed by the method of Yang et al. (2000b). The results suggest that the present vertebrate PGIs are at evolutionary stasis and are being subjected to intense purifying selection. The purifying selection is to maintain polarity and volume of the protein but not the charge groups of amino acids. Phylogenetic analysis reveals that vertebrate PGIs can be classified into three major groups: the mammalian, amphibian-reptilian, and teleostean PGIs. The gene tree suggests that the gene duplication event of PGI in bonyfishes occurred before diversification of Acanthopterygii but after the split of bonyfishes and tetrapods. The evolution of multiple functions of PGI is discussed.

The minisatellite of the GPI/AMF/NLK/MF gene: interspecies conservation and transcriptional activity

Minisatellites are tandemly repeated DNA sequences found throughout the genomes of all eukaryotes. They are regions often prone to instability and hence hypervariability; thus repeat unit sequence is generally not conserved beyond closely related species. We have studied the minisatellite located in intron 9 of the human glucose phosphate isomerase (GPI) gene (also known as neuroleukin, autocrine motility factor, maturation and differentiation factor) and have found, by Zoo blotting coupled with PCR amplification and DNA sequencing, that similar repeat units are present in seven other species of mammal. There is also evidence for the presence of the minisatellite in chicken. The repeat unit does not appear to be present at any other locus in these genomes. Minisatellite DNA has been reported to be involved in recombination activity, control of gene expression of nearby gene(s) (both transcriptional and translational), whilst others form protein coding regions. The high level of conservation exhibited by the GPI minisatellite, coupled with the unique location, strongly suggests a functional role. Our results from transient and stable transfections using luciferase reporter constructs have shown that the GPI minisatellite region can act to increase transcription from the SV40 promoter, CMV promoter and the human GPI promoter.

Purification and characterization of a proteinase inhibitor from white croaker skeletal muscle (Micropogon opercularis)

A trypsin proteinase inhibitor has been purified to homogeneity from the skeletal muscle of white croaker (Micropogon opercularis). Previously, we had described the occurrence in fish muscle of a serine protease (proteinase I) which showed a great capacity to degrade whole myofibrils in vitro and an endogenous inhibitor that prevented the action of the protease, both on natural and artificial substrates. In this paper, we report the purification and further biochemical characterization of the endogenous trypsin inhibitor. The purification was carried out by DEAE-Sephacel, Con A-Sepharose, Sephacryl S-300 and Mono Q. Throughout the purification procedure, trypsin inhibitory activity was assayed using azocasein as substrate. The molecular mass of the inhibitor was 65 kDa, as estimated by SDS-PAGE and gel filtration. The trypsin inhibitor is a glycoprotein, as deduced by the fact that it binds to Con A-Sepharose and stains with PAS and showed a wide range of pH stability (from 5 to 11). The thermal stability of the inhibitor considerably decreased at temperatures >60 degrees C. Assays of the inhibitor against various proteases indicated that it is highly specific for serine proteases, since it did not inhibit proteases belonging to any other groups. The inhibitor was able to inhibit the endogenous target enzyme (proteinase I) in a dose-dependent manner, with a 50% inhibition at a molar ratio close to 1. The present work contributes to improving our understanding of the physiological role of the proteinase I-inhibitor system in muscle protein breakdown, as well as its influence on post mortem proteolysis.

The crystal structure of human phosphoglucose isomerase at 1.6 Å resolution: implications for catalytic mechanism, cytokine activity and haemolytic anaemia

Phosphoglucose isomerase (PGI) is a multifunctional protein, which, inside the cell, functions as a housekeeping enzyme of glycolysis and gluconeogenesis and, outside the cell, exerts wholly unrelated cytokine properties. We have determined the structure of human PGI to a resolution of 1.6 A using X-ray crystallography. The structure is highly similar to other PGIs, especially the architecture of the active site. Fortuitous binding of a sulphate molecule from the crystallisation solution has facilitated an accurate description of the substrate phosphate-binding site. Comparison with both native and inhibitor-bound rabbit PGI structures shows that two loops move closer to the active site upon binding inhibitor. Interestingly, the human structure most closely resembles the inhibitor-bound structure, suggesting that binding of the phosphate moiety of the substrate may trigger this conformational change. We suggest a new mechanism for catalysis that uses Glu357 as the base catalyst for the isomerase reaction rather than His388 as proposed previously. The human PGI structure has also provided a detailed framework with which to map mutations associated with non-spherocytic haemolytic anaemia.

Paradigms of growth in fish

Most fish are indeterminate growers with white muscle making up the majority of the acquired bulk. Within the muscle, the myofibrillar fraction accounts for almost two-thirds of the protein synthetic activity, implying that it is accretion of myofibrillar proteins that makes the single most important contribution to fish growth. Fish muscle growth itself is not linear and occurs through a combination of hyperplasia and hypertrophy in post-juvenile stages. Superimposed on periodicity of growth in length and mass can be other phases governed by lunar, reproductive or circannual cycles. Data on fish growth are discussed in the framework of site-specific muscle abundance, metabolic and functional zonation of muscle, proliferation and differentiation of satellite cells and the contribution of myofibrillar proteins. Hormonal control of muscle growth is described against the backdrop of plasma availability of myogens (insulin, IGF-I, growth hormone), distribution and dynamics of their respective receptors, and their interactions. Important contributions of the 'supply side' are discussed with hormones regulating amino acid resorption from the intestine, intestinal growth, liver processing and amino acid uptake by the muscle. Data are also interpreted from metabolic angles, to explain lipolytic and nitrogen-sparing effects of growth hormones, and lipogenic effects of insulin and high protein diets. Finally, special attention is devoted to the multifaceted roles of arginine in fish growth, as precursor, intermediate and hormone secretagogue.

Purification of a novel myofibril-bound serine proteinase inhibitor (MBSPI) from the skeletal muscle of lizard fish

A novel myofibril-bound serine proteinase inhibitor (MBSPI) was purified to homogeneity from the skeletal muscle of lizard fish (Saurida wanieso). Purification was carried out by ammonium sulfate fractionation, followed by column chromatographies on DEAE-Sephacel, SP-Sepharose and Sephadex G-150. MBSPI was purified 7.7-fold starting from the DEAE-Sephacel fraction, with a yield of 0.2%. It is a monomeric protein with the molecular mass of 50 kDa as estimated by SDS-PAGE and gel filtration. MBSPI reveals high inhibition specificity toward a myofibril-bound serine proteinase (MBSP) purified from lizard fish muscle. No inhibition is detected toward bovine trypsin, bovine chymotrypsin, two trypsins from carp hepatopancreas and a serine proteinase isolated from the sarcoplasmic fraction of white croaker muscle. It does not exert any inhibitory activity toward a myofibril-bound serine proteinase from carp muscle.