**3. Major surface protease: (MSP) GP63**

GP63 is known leishmanolysin or called major surface protease (MSP) or promastigote surface protease (PSP), also called a zinc- dependent metalloprotease [50, 61, 62]. It is found at *Leishmania* surface connected through a glycophosphatidylinositol (GPI) anchor, or is direct secreted to an extracellular surrounding [50]. Fracture of GPI anchor by phospholipase C leads up to scattering gp63 in extracellular space, also is secreted directly by the flagellar pocket, as well as the presence of GP63 in intracellular pools [63].

GP63s are encoded by multiple genes that appear vary in their sequence (especially in untranslated regions), array in the *Leishmania* genome [63, 64]. Differences in the untranslated regions may lead to different gene expression [50]. These genes generate abundant proteins which lead to vary among species and forms of *Leishmania* that cause a different biological effect [65]. Genes of gp63 are expressed in promastigotes and amastigotes [61]. It is expressed in metacyclic more abundantly than procyclic promastigotes [62]. Also, gp63 has been observed at lower levels through its expression in amastigotes [50].

GP63 is a multifunction enzyme that related to an inhibition of complement components. The recent findings refer to a critical role played by gp63 as an important virulence factor that wide influence cellular signaling mechanisms and related pathways [65]. GP63 is responsible about migration of parasite through extracellular matrix, avoid lysis by the complement system, evasion from macrophagic intracellular hydrolysis [61] and facilitation of promastigotes phagocytosis by macrophage, matrix extracellular degradation, contribute to intracellular migration, NK inhibition and persistence and progression of infection [64, 66]. Also, inhibit nitric oxide production (Leishmanicidal) or macrophages pro-inflammatory cytokines [67].

This protease serves to cleaves complement protein C3b and converts to C3bi (inactivated form of C3b) and protects promastigote from complement-mediated lysis. Further, generation of C3bi leads to uptake promastigote by complement receptors such as CR3 which located at the surface of macrophage. The evidence suggests, promastigote ligates CR3 directly and via opsonized C3bi [7, 62]. C3bi acts as a bridge between complement receptor at surface of macrophage and gp63- bearing promastigote [68]. C3bi generation by enzymatic activity of gp63 bonded to promastigote surface, mediate phagocytosis process by complement receptors (CR1 andCR3) that leading to silent entry of parasite into macrophage [7, 62].

GP63 has been described to is not only to degradation and damage of transcription factors and various kinases, but also it modulates negative regulatory mechanisms of signaling pathways for example protein tyrosine phosphatases (PTP). Activation of PTP together with other signaling molecules leading to inhibition of leishmanicidal and inflammatory functions [63, 65]. GP63 is activate protein tyrosine phosphatases that result alteration of MAP, JAK, STAT1 and IRAK-1kinase pathways. In the nucleus, it is responsible for the inactivation of important transcription factors which activate specific chemokines, such as NF-κB [9, 65].

#### **4. Cysteine proteinases (CPs)**

Cysteine proteases (CPs) are degrading enzymes which cleave various proteins. They are act as essential virulence factors in leishmanial infection, as well play an important role in many pathogenic protozoa and other microorganisms [69]. At least from 6 classes proteases classified in the proteolysis: serine, cysteine, glutamate, metallo, threonine and aspartate proteases. Cysteine proteases (CPs) are classified into 72 families, so not all are expressed in parasitic protozoa [70]. In *Leishmania* genome, there are 154 peptidases include cysteine, aspartic, serine and metalloproteases. *Leishmania* protease are necessary for continuation and establishment of infection [71]. In several pathogenic organisms, including parasitic protozoa as *Entamoeba histolytica*, *Leishmania* and *Trypanosoma*, found CPs which are enzymes [72, 73]. *Leishmania* has three types from CPs: CPA, CPB, and CPC [72, 74]. CPs are expressed in higher levels in the mammalian amastigote [70]. Gene expression of CPA is maximal level in amastigote stage, while lower expression is in promastigote [73]. Also, CPB is expressed at high levels in the amastigote, is expressed at a very few level in procyclic-promastigotes [75]. CPB1 and CPB2 are expressed in higher levels of metacyclic promastigote, while CPC in procyclicpromastigote [70].

Although roles of CPs in pathogenesis of *Leishmania* are unclear, it has been showed that Leishmaniasis cannot continue in macrophages with the presence of *Geographical Distribution of Cutaneous Leishmaniasis and Pathogenesis DOI: http://dx.doi.org/10.5772/intechopen.101841*

CP inhibitors [76]. Cysteine proteases play key roles in *Leishmania* biology and their inhibition is appearing as an important strategy to the elimination of the disease. They are necessary to metabolism, intracellular survival and reproduction of parasite [74], participate in exsheathing, excystment, also tissue invasion and some parasite immune-evasion [69]. CPs appears an essential role in pathogenicity and leads multi-processes such as modulation or evasion of the host immune response, cell/tissue degradation and damage, catalyze hydrolysis of various host proteins that are responsible of important cellular biological activities in pathways, differentiation of promastigote to amastigote and autophagy [70, 71]. Generally, CPA lead an essential key in the interactions of parasite with host cell [43, 77], while CPB modulates Th1 immune responses, and IFN-γ production via damage of transcription factor (NF- κB) and inhibition ofIL-12 production. Also CPB is modulate levels of parasite proteins as gp63 [70].

The inhibition of CPA and CPB or deletion their genes not only alters autophagy pathway but too prevents transformation into amastigotes, thus support hypothesis of autophagy is required for the differentiation [43, 78]. Parasites evidenced low growth, pathogenicity and efficacy after their treated with CP inhibitors [79]. There are efforts towards make it as vaccine candidates because their potential and their importance. For now, no effective drug or vaccine for leishmaniasis [69, 71, 74].
