proteaseinhibition

Prevention of proteases by a multifunctional plasma protein: alpha-2 macroglobulin (A2M), can protect us from many diseases.

Mohammad M. Khan, MBBS., PhD. Biomark Bangladesh Foundation, Hosna Centre, Gulshan Avenue, Gulshan, Dhaka 1212, Bangladesh. Author contact: aurnobaunton@gmail.com

Reviewed by Naseem Mahmud, MBBS, PhD, DTM, Obstetrics and Gynaecology, United Hospital, Dhaka, Bangladesh.

INTRODUCTION

Previously we have shown (in online Journal, www.rarediseaseindia.org: www.rarediseasesindia.org/septicshock, 2012)1 - first time in the world - that alpha-2-macroglobulin (A2M) is the major innate immune factor against foreign protease and exogenous A2M is a major life saving protein in the critical stage of protease induced septic shock animal models2-5. Recently, in a successful treatment with A2M in osteoarthritis was also shown in human subjects6.  Now we are showing the importance of different kind of protease(s) involvement in many common and rare diseases and the treatment with multifunctional broad spectrum protease inhibitor, A2M could be a life saving molecule in the field of medicine7-8 (Fig.1). We also suggest to include A2M - as a major component in the innate immune system.

A2M 

A2M, a broad spectrum protease inhibitor, normally is continuously removing proteases, and keep us healthy7,8,21. But if the protease concentration goes up and A2M is consumed and fail to clear proteases due to less supply to its demand from its original source (liver), then proteases have free access to cleave other proteins of many different systems and start inactivating all of our defense mechanisms. Eventually many toxic molecules are generated and we become sick. At this stage, it is essential to supply more A2M to compensate and remove proteases from body4,5.

Low level of A2M are well documented indicate a relationship of disproportion of proteases and protease inhibitor in the patho-physiology of many disease processes22. In animal research it was also clearly documented that in a Gram negative bacterial septic shock model, level of A2M went down to 30% of its original concentration and remaining 30% of A2M was not enough to protect animals from death. In that study, injecting purified A2M at the very crisis stage of septic shock was able to rescue animals from death which worked as a life saving medicine4,5.

A2M, an extraordinary multifunctional blood protein had never been got any attention for a possibility as a life saving therapeutic use in the field of medicine. Therefore, measurement of serum/plasma A2M concentration and different kind of proteases in patients may be a very important indicator for the diagnosis and speculate the severity of disease process. The life saving role of A2M was first described in a bacterial protease induced septic shock animal models 1-4. It was also shown that one of the major mechanisms for cause of septic shock followed by death was through the activation of plasma kallikrein-kinin system in which bradykinin was released from high molecular weight kininogen by bacterial protease2-3. In that study it was clearly shown that bacterial protease can generate maximum amount of bradykinin within 5 seconds in plasma in the presence of kininase I and II inhibitor (ortho-phenthroloine) in vitro3. In presence of bradykinin receptor antagonist also showed complete inhibition of severe hypotension and shock followed by death in protease induced shock model3.

Proteins of the A2M family are present in a variety of animal phyla, including the nematodes, arthropods, mollusks, echinoderms, urochordates, and vertebrates and invertebrates or even plant kingdom9. A shared suite of unique functional characteristics have been documented for the A2Ms of vertebrates, arthropods, and mollusks. The A2Ms of nematodes, arthropods, mollusks show significant sequence identity in key functional domains. Thus, the A2Ms comprise an evolutionarily conserved arm of the innate immune system with similar structure and function in animal phyla separated by 0.6 billion years of evolution9. A2M prevents protease induced activation of coagulation by inhibiting thrombin and inhibitor of fibrinolysis by inhibiting plasmin and kallikrein. Numerous growth factors, cytokines and hormones bind to A2M.  A2M also binds soluble beta-amyloid, of which it mediates degradation as seen in the brain of Alzheimer's disease (AD) patients. A2M is synthesized mainly in liver, but also locally by macrophages, fibroblasts, and adrenocortical cells.A2M is also produced in the brain where it binds multiple extracellular ligands and is internalized by neurons and astrocytes23-28.

A2M: First line of defense protein in our innate immune system (suggestion)

Mechanism of inhibition of proteases by A2M (Table 2): Proteases are currently classified into six broad groups: Serine proteases, Threonine proteases, Cysteine proteases, Aspartate proteases, Metalloproteases and Glutamic acid proteases29.

The protease inhibitors are of two classes30, the active-site inhibitors and the α2-macroglobulins. Inhibitors for the first class bind and inactivate the active site of the target protease. Proteins of the second class bind proteases by a unique molecular trap mechanism and deliver the bound protease to a receptor-mediated endocytic system for degradation in secondary lysosomes.

In human plasma, concentration of A2M is 2-4 mg/ml.  Its molecular size is 720 kDa. A2M is composed of four identical subunits bound together by -S-S- bonds. A2M has in its structure a 35 amino acid "bait" region. Proteases binding and cleaving the bait region become bound proteinase-A2M complex. The proteinase-A2M complex is recognized by macrophage receptors and cleared from the system21. 

30.  "Evolutionary families of peptidase inhibitors". Biochem. J. 378(Pt 3): 705–716.

 Submitted to Rare Diseases India on July 14, 2015.

Book on this subject:

A2M-Miracle Protein, the lifesaver By Mohammad Khan MBBS PhD

Publication Date: January 15, 2017

Book Size: 6" x 9"

Pages: 51

Binding: Spiral Bound

ISBN: 9781946634290