Membrane-associated zinc peptidase families: comparing ACE and ACE2

beta-Amyloid degradation and Alzheimer's disease

Extensive β-amyloid (Aβ) deposits in brain parenchyma in the form of senile plaques and in blood vessels in the form of amyloid angiopathy are pathological hallmarks of Alzheimer's disease (AD). The mechanisms underlying Aβ deposition remain unclear. Major efforts have focused on Aβ production, but there is little to suggest that increased production of Aβ plays a role in Aβ deposition, except for rare familial forms of AD. Thus, other mechanisms must be involved in the accumulation of Aβ in AD. Recent data shows that impaired clearance may play an important role in Aβ accumulation in the pathogenesis of AD. This review focuses on our current knowledge of Aβ-degrading enzymes, including neprilysin (NEP), endothelin-converting enzyme (ECE), insulin-degrading enzyme (IDE), angiotensin-converting enzyme (ACE), and the plasmin/uPA/tPA system as they relate to amyloid deposition in AD.

Renin-angiotensin system in human coronavirus pathogenesis

Although initially considered relatively harmless pathogens, human coronaviruses (HCoVs) are nowadays known to be associated with more severe clinical complications. Still, their precise pathogenic potential is largely unknown, particularly regarding the most recently identified species HCoV-NL63 and HCoV-HKU1. HCoVs need host cell proteins to successively establish infections. Proteases of the renin–angiotensin system serve as receptors needed for entry into target cells; this article describes the current knowledge on the involvement of this system in HCoV pathogenesis.

Zinc status and vacuolar zinc transporters control alkaline phosphatase accumulation and activity in Saccharomyces cerevisiae

Little is known about how metalloproteins in the secretory pathway obtain their metal ion cofactors. We used the Pho8 alkaline phosphatase of the yeast Saccharomyces cerevisiae to probe this process in vivo. We found that both Pho8 activity and protein accumulation are zinc-dependent and decrease in zinc-limited cells. Low Pho8 accumulation was the result of degradation by vacuolar proteases. Surprisingly, the protective effect of zinc on Pho8 stability was not solely due to Zn(2+) binding to the active-site ligands suggesting that the Pho8 protein is targeted for degradation in zinc-limited cells by another mechanism. Pho8 appears to be a rare example of a metalloprotein whose stability is regulated by its metal cofactor independently of active-site binding. We also assessed which zinc transporters are responsible for supplying zinc to Pho8. We found that the Zrc1 and Cot1 vacuolar zinc transporters play the major role while the Msc2/Zrg17 zinc transporter complex active in the endoplasmic reticulum is not involved. These results demonstrate that the vacuolar zinc transporters, previously implicated in metal detoxification, also deliver zinc to certain metalloproteins within intracellular compartments. These data suggest that Pho8 receives its metal cofactor in the vacuole rather than in earlier compartments of the secretory pathway.

Angiotensin-converting enzyme levels and activity in Alzheimer's disease: differences in brain and CSF ACE and association with ACE1 genotypes

Angiotensin-converting enzyme (ACE) has been implicated in Alzheimer's disease (AD): ACE1 variations influence plasma ACE and risk of AD, and ACE is increased in AD brain. We measured frontal ACE level and activity in 89 AD and 51 control brains, and post-mortem CSF from 101 cases and 19 controls. Neuron-specific enolase (NSE) level and Braak stage were used to indicate neuronal preservation and disease progression. We genotyped the common ACE insertion/deletion polymorphism, rs4343, rs1800764 and rs4921. ACE activity was elevated in AD and correlated with Braak stage. Crude ACE levels were unchanged but adjustment for NSE suggested increased neuronal ACE production with Braak stage. Exposing SH-SY-5Y neurons to oligomeric Abeta1-42 increased ACE level and activity, suggesting Abeta may upregulate ACE in AD. In CSF, ACE level but not activity was reduced in AD. ACE1 genotype did not predict ACE level or activity in brain or CSF. ACE activity and neuronal production increase in AD brain, possibly in response to Abeta. Peripheral measurements do not reflect ACE activity in the brain.

The Role of Neuropeptide Endopeptidases in Cutaneous Immunity

Proteolytic processing and degradation plays an important role in modulating the generation and bioactivity of neuroendocrine peptide mediators, a class of key molecules in cutaneous biology.

Accordingly, the cellular localization and expression, and the molecular biology and structural properties of selected intracellular prohormone convertases and ectopically expressed zinc-binding metalloendoproteases are discussed.

A special reference will be made to the physiologic and pathophysiologic significance of these endopeptidases in cutaneous immunobiology.

Because of the number of pathologically relevant changes in inflammation and tumor progression that can be directly attributed to neprilysin and angiotensin-converting enzyme, a particular focus will be on the role of these enzymes in modulating innate and adaptive immune responses in the skin.

New aspects of the renin-angiotensin system: angiotensin-converting enzyme 2 - a potential target for treatment of hypertension and diabetic nephropathy

PURPOSE OF REVIEW

Whereas angiotensin-converting enzyme promotes the formation of angiotensin II, angiotensin-converting enzyme 2 promotes the degradation of angiotensin II to angiotensin-(1-7). We review recent studies dealing with angiotensin-converting enzyme 2 in kidney disease and hypertension, and discuss the potential therapeutic benefit of increasing angiotensin-converting enzyme 2 activity in the treatment of these diseases.

RECENT FINDINGS

In glomeruli from diabetic mice, angiotensin-converting enzyme 2 expression is downregulated, and pharmacological inhibition of angiotensin-converting enzyme 2 leads to worsening of albuminuria, increased mesangial matrix deposition and fibronectin expression. The deletion of the angiotensin-converting enzyme 2 gene in mice leads to worsening of angiotensin II-induced hypertension and has also been shown to cause glomerulosclerosis in aging male mice.

SUMMARY

Angiotensin-converting enzyme 2 is a key enzyme in the renin-angiotensin system that favors the degradation of angiotensin I and angiotensin II. Angiotensin-converting enzyme 2 inhibition by pharmacological means and by genetic deletion worsens kidney disease in diabetic mice. Strategies geared to increasing angiotensin-converting enzyme 2 activity may provide a novel therapeutic target within the renin-angiotensin system by enhancing angiotensin II degradation that may complement the current approach of inhibiting angiotensin II formation and action. Amplifying angiotensin-converting enzyme 2 activity may have a potential therapeutic role for kidney disease and hypertension.

Overexpression of ACE2 Enhances Plaque Stability in a Rabbit Model of Atherosclerosis

Objective— The purpose of this study was to test the hypothesis that ACE2 overexpression may enhance atherosclerotic plaque stability by antagonizing ACE activity and converting angiotensin II to angiotensin 1–7.

Methods and Results— Atherosclerotic plaques were induced in the abdominal aorta of 114 rabbits by endothelial injury and atherogenic diet. Gene therapy was performed in group A at week 4 and in group B at week 12, respectively. Each group of rabbits were randomly divided into 3 subgroups which received, respectively, a recombinant ACE2 expressing vector (AdACE2), a control vector AdEGFP and AdACE2+A779, an antagonist of angiotensin 1–7 receptor. Local ACE2 overexpression attenuated the progression of lesions from week 4 to week 8, but not progression of plaque size from week 12 to week 16. In group B rabbits, local ACE2 overexpression resulted in stable plaque compositions, ie, fewer macrophages, less lipid deposition and more collagen contents, higher plaque stability scores, decreased angiotensin II levels, and increased angiotensin 1–7 levels in plaque tissues in the AdACE2 subgroup compared with those in the AdEGFP subgroup.

Conclusions— Overexpression of ACE2 results in stabilized atherosclerotic plaques and the mechanism is probably the conversion of vasoconstrictive angiotensin II to vessel protective angiotensin 1–7.

Enzymatic pathways of the brain renin-angiotensin system: unsolved problems and continuing challenges

The brain renin-angiotensin system continues to be enigmatic more than 40 years after the brain was first recognized to be a site of action of angiotensin II. This review focuses on the enzymatic pathways for the formation and degradation of the growing number of active angiotensins in the brain. A brief description and nomenclature of the peptidases involved in the processing of angiotensin peptides in the brain is given. Of primary interest is the array of enzymes that degrade radiolabeled angiotensins in receptor binding assays. This poses major challenges to studies of brain angiotensin receptors and it is debatable whether an accurate determination of brain angiotensin receptor binding kinetics has yet been made. The quandary facing the investigator of brain angiotensin receptors is the need to protect the radioligand from metabolic alteration while maintaining the characteristics of the receptors in situ. It is the tenet of this review that we have yet to fully understand the binding characteristics of brain angiotensin receptors and the extent of their distribution in the brain because of our inability to fully protect the angiotensins from metabolic alteration until equilibrium binding conditions can be attained.

Computational characterization and design of SARS coronavirus receptor recognition and antibody neutralization

The sequential determination of crystal structures of the SARS coronavirus spike receptor-binding domain (RBD) in complex with its cellular receptor or neutralizing antibody opened a door for the design and development of antiviral competitive inhibitors. Based on those complex structures, we conduct computational characterization and design of RBD-mediated receptor recognition and antibody neutralization. The comparisons between computational predictions and experimental evidences validate our structural bioinformatics protocols. And the calculations predict a number of single substitutions on RBD, receptor or antibody that could remarkably elevate the binding affinities of those complexes. It is reasonable to anticipate our structure-based computation-derived hypotheses could be informative to the future biochemical and immunological tests.

Two metallocarboxypeptidases from the protozoan Trypanosoma cruzi belong to the M32 family, found so far only in prokaryotes

MCPs (metallocarboxypeptidases) of the M32 family of peptidases have been identified in a number of prokaryotic organisms, and only a few of them have been characterized biochemically. Members of this family are absent from eukaryotic genomes, with the remarkable exception of those of trypanosomatids. The genome of the CL Brener clone of Trypanosoma cruzi, the causative agent of Chagas' disease, encodes two such MCPs, with 64% identity between them: TcMCP-1 and TcMCP-2. Both genes, which are present in a single copy per haploid genome, were expressed in Escherichia coli as catalytically active polyHis-tagged recombinant enzymes. Despite their identity, the purified TcMCPs displayed marked biochemical differences. TcMCP-1 acted optimally at pH 6.2 on FA {N-(3-[2-furyl]acryloyl)}-Ala-Lys with a K(m) of 166 muM. Activity against benzyloxycarbonyl-Ala-Xaa substrates revealed a P1' preference for basic C-terminal residues. In contrast, TcMCP-2 preferred aromatic and aliphatic residues at this position. The K(m) value for FA-Phe-Phe at pH 7.6 was 24 muM. Therefore the specificities of both MCPs are complementary. Western blot analysis revealed a different pattern of expression for both enzymes: whereas TcMCP-1 is present in all life cycle stages of T. cruzi, TcMCP-2 is mainly expressed in the stages that occur in the invertebrate host. Indirect immunofluorescence experiments suggest that both proteins are localized in the parasite cytosol. Members of this family have been identified in other trypanosomatids, which so far are the only group of eukaryotes encoding M32 MCPs. This fact makes these enzymes an attractive potential target for drug development against these organisms.

Manipulating the angiotensin system--new approaches to the treatment of solid tumours

Angiotensin II (Ang II), a main effector peptide in the renin-angiotensin system (RAS), plays a fundamental role as a vasoconstrictor in controlling cardiovascular function and renal homeostasis. Ang II also acts as a growth promoter or angiogenic factor via type 1 angiotensin II receptors (AT1Rs) in certain tumour cell lines. Recent studies have shown the activation of the local RAS in various tumour tissues, including the abundant generation of Ang II by angiotensin-converting enzyme (ACE) and the upregulation of AT1R expression. Thus, considerable attention has been paid to the role of the RAS in cancer and its blockade as a new approach to the treatment of cancer. There is increasing evidence that the Ang II-AT1R system is involved in tumour growth, angiogenesis and metastasis in experimental models, suggesting the therapeutic potential of an ACE inhibitor and AT1R blocker, both of which have been used as antihypertensive drugs. In addition, specific Ang II-degrading enzymes are expressed in tumours and play a regulatory role in cell proliferation and invasion. This review focuses on the role of the Ang II-AT1R system in solid tumours, particularly in the progression of gynaecological cancer, and presents the clinical potential of manipulating the angiotensin system as a novel and promising strategy for cancer treatment.

Identification of critical active-site residues in angiotensin-converting enzyme-2 (ACE2) by site-directed mutagenesis

Angiotensin‐converting enzyme‐2 (ACE2) may play an important role in cardiorenal disease and it has also been implicated as a cellular receptor for the severe acute respiratory syndrome (SARS) virus. The ACE2 active‐site model and its crystal structure, which was solved recently, highlighted key differences between ACE2 and its counterpart angiotensin‐converting enzyme (ACE), which are responsible for their differing substrate and inhibitor sensitivities. In this study the role of ACE2 active‐site residues was explored by site‐directed mutagenesis. Arg273 was found to be critical for substrate binding such that its replacement causes enzyme activity to be abolished. Although both His505 and His345 are involved in catalysis, it is His345 and not His505 that acts as the hydrogen bond donor/acceptor in the formation of the tetrahedral peptide intermediate. The difference in chloride sensitivity between ACE2 and ACE was investigated, and the absence of a second chloride‐binding site (CL2) in ACE2 confirmed. Thus ACE2 has only one chloride‐binding site (CL1) whereas ACE has two sites. This is the first study to address the differences that exist between ACE2 and ACE at the molecular level. The results can be applied to future studies aimed at unravelling the role of ACE2, relative to ACE, in vivo.