Yama/CPP32β, a mammalian homolog of CED-3, is a CrmA-inhibitable protease that cleaves the death substrate poly(ADP-ribose) polymerase

Caspases, which are the executioners of apoptosis, comprise two distinct classes, the initiators and the effectors. Although general structural features are shared between the initiator and the effector caspases, their activation, inhibition and release of inhibition are differentially regulated. Biochemical and structural studies have led to important advances in understanding the underlying molecular mechanisms of caspase regulation. This article reviews these latest advances and describes our present understanding of caspase regulation during apoptosis.

Molecular mechanisms of caspase regulation during apoptosis

Heparin, a sulfated polysaccharide belonging to the family of glycosaminoglycans, has numerous important biological activities, associated with its interaction with diverse proteins. Heparin is widely used as an anticoagulant drug based on its ability to accelerate the rate at which antithrombin inhibits serine proteases in the blood coagulation cascade. Heparin and the structurally related heparan sulfate are complex linear polymers comprised of a mixture of chains of different length, having variable sequences. Heparan sulfate is ubiquitously distributed on the surfaces of animal cells and in the extracellular matrix. It also mediates various physiologic and pathophysiologic processes. Difficulties in evaluating the role of heparin and heparan sulfate in vivo may be partly ascribed to ignorance of the detailed structure and sequence of these polysaccharides. In addition, the understanding of carbohydrate-protein interactions has lagged behind that of the more thoroughly studied protein-protein and protein-nucleic acid interactions. The recent extensive studies on the structural, kinetic, and thermodynamic aspects of the protein binding of heparin and heparan sulfate have led to an improved understanding of heparin-protein interactions. A high degree of specificity could be identified in many of these interactions. An understanding of these interactions at the molecular level is of fundamental importance in the design of new highly specific therapeutic agents. This review focuses on aspects of heparin structure and conformation, which are important for its interactions with proteins. It also describes the interaction of heparin and heparan sulfate with selected families of heparin-binding proteins.

http://www-heparin.rpi.edu/main/files/papers/4f1623c54d6ab5.21304086.pdf

Heparin-protein interactions

Almost one-third of all proteases can be classified as serine proteases, named for the nucleophilic Ser residue at the active site. This mechanistic class was originally distinguished by the presence of the AspHis-Ser “charge relay” system or “catalytic triad”.1 The Asp-His-Ser triad can be found in at least four different structural contexts, indicating that this catalytic machinery has evolved on at least four separate occasions.2 These four clans of serine proteases are typified by chymotrypsin, subtilisin, carboxypeptidase Y, and Clp protease (MEROPS nomenclature;3 Table 1). More recently, serine proteases with novel catalytic triads and dyads have been discovered, including Ser-His-Glu, Ser-Lys/His, His-Ser-His, and N-terminal Ser.2 Several of these novel serine proteases are subjects of accompanying articles in this issue. This article will review recent work on the mechanism and specificity of chymotrypsin-like enzymes, with the occasional references to pertinent experiments with subtilisin. Chymotrypsin-like proteases are the most abundant in nature, with over 240 proteases recognized in the MEROPS database.3 * E-mail: hedstrom@brandeis.edu; phone: 781-736-2333; FAX: 781-736-2349. 4501 Chem. Rev. 2002, 102, 4501−4523

Serine protease mechanism and specificity

The American Heart Association, in conjunction with the National Institutes of Health, annually reports the most up-to-date statistics related to heart disease, stroke, and cardiovascular risk factors, including core health behaviors (smoking, physical activity, diet, and weight) and health factors (cholesterol, blood pressure, and glucose control) that contribute to cardiovascular health. The Statistical Update presents the latest data on a range of major clinical heart and circulatory disease conditions (including stroke, congenital heart disease, rhythm disorders, subclinical atherosclerosis, coronary heart disease, heart failure, valvular disease, venous disease, and peripheral artery disease) and the associated outcomes (including quality of care, procedures, and economic costs).The American Heart Association, through its Statistics Committee, continuously monitors and evaluates sources of data on heart disease and stroke in the United States to provide the most current information available in the annual Statistical Update. The 2022 Statistical Update is the product of a full year's worth of effort by dedicated volunteer clinicians and scientists, committed government professionals, and American Heart Association staff members. This year's edition includes data on the monitoring and benefits of cardiovascular health in the population and an enhanced focus on social determinants of health, adverse pregnancy outcomes, vascular contributions to brain health, and the global burden of cardiovascular disease and healthy life expectancy.Each of the chapters in the Statistical Update focuses on a different topic related to heart disease and stroke statistics.The Statistical Update represents a critical resource for the lay public, policymakers, media professionals, clinicians, health care administrators, researchers, health advocates, and others seeking the best available data on these factors and conditions. 

https://www.ahajournals.org/doi/pdf/10.1161/CIR.0000000000001052

Heart Disease and Stroke Statistics—2022 Update: A Report From the American Heart Association

Loop-Sheet Mechanism of Serpin Polymerization Tested by Reactive Center Loop Mutations

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/jth.13171

Discovery and characterization of an antibody directed against exosite I of thrombin

The classical pathway of complement is crucial to the immune system, but it also contributes to inflammatory diseases when dysregulated. Binding of the C1 complex to ligands activates the pathway by inducing autoactivation of associated C1r, after which C1r activates C1s. C1s cleaves complement component C4 and then C2 to cause full activation of the system. The interaction between C1s and C4 involves active site and exosite-mediated events, but the molecular details are unknown. In this study, we identified four positively charged amino acids on the serine protease domain that appear to form a catalytic exosite that is required for efficient cleavage of C4. These residues are coincidentally involved in coordinating a sulfate ion in the crystal structure of the protease. Together with other evidence, this pointed to the involvement of sulfate ions in the interaction with the C4 substrate, and we showed that the protease interacts with a peptide from C4 containing three sulfotyrosine residues. We present a molecular model for the interaction between C1s and C4 that provides support for the above data and poses questions for future research into this aspect of complement activation.

Identification of a Catalytic Exosite for Complement Component C4 on the Serine Protease Domain of C1s

The serpins differ from the many other families of serine protease inhibitors in that they undergo a profound change in topology in order to entrap their target protease in an irreversible complex. The solving of the structure of this complex has now provided a video depiction of the changes involved. Cleavage of the exposed reactive centre of the serpin triggers an opening of the five-stranded A-sheet of the molecule, with insertion of the cleaved reactive loop as an additional strand in the centre of the sheet. The drastic displacement of the acyl-linked protease grossly disrupts its active site and gives an overall loss of 40% of ordered structure. This ability to provide effectively irreversible inhibition explains the selection of the serpins to control the proteolytic cascades of higher organisms. The conformational mechanism provides another advantage in its potential to modulate activity. Sequential crystallographic structures now provide clear depictions of the way antithrombin is activated on binding to the heparans of the microcirculation, and how evolution has utilized this mobile mechanism for subtle variations in activity. The complexity of these modulatory mechanisms is exemplified by heparin cofactor II, where the change in fold is seen to trigger multiple allosteric effects. The downside of the mobile mechanism of the serpins is their vulnerability to aberrant intermolecular ϐ-linkages, resulting in various disorders from cirrhosis to thrombosis. These provide a well defined structural prototype for the new entity of the conformational diseases, including the common dementias, as confirmed by the recent identification of the familial neuroserpin dementias.

James A. Huntington

Papers

Loop-Sheet Mechanism of Serpin Polymerization Tested by Reactive Center Loop Mutations

Discovery and characterization of an antibody directed against exosite I of thrombin

Identification of a Catalytic Exosite for Complement Component C4 on the Serine Protease Domain of C1s

How serpins change their fold for better and for worse.

The Effect of a Reducing-end Extension on Pentasaccharide Binding by Antithrombin