Murine serine proteases MASP-1 and MASP-3, components of the lectin pathway activation complex of complement, are encoded by a single structural gene

Abstract

Activation of the lectin pathway of complement is initiated by the binding to microbial carbohydrate structures of a multimolecular fluid-phase complex composed of a carbohydrate recognition subcomponent that associates with three specific serine proteases and an enzymatically inert protein of 19 kDa. The first carbohydrate recognition subcomponent of the lectin pathway identified was mannan-binding lectin (MBL), hence the serine proteases were named MBL-associated serine proteases (MASPs) and numbered according to the sequence of their discovery. Here we describe the primary structures of the two distinct serine proteases MASP-1 and MASP-3 in the rat (and of MASP-3 in the mouse), show their association with plasma MBL complexes, and demonstrate that in rat and mouse, as in man, MASP-1 and MASP-3 are encoded by a single structural gene. For both species, we present the genomic region and regulatory elements responsible for the processing of either MASP-1 or MASP-3 mRNA by alternative splicing/alternative polyadenylation. Furthermore, we demonstrate the evolutionary conservation of MASP-3 mRNA in cDNA transcripts from guinea pig, rabbit, pufferfish, and cow.

Composition of the Lectin Pathway of Complement inGallus gallus: Absence of Mannan-Binding Lectin-Associated Serine Protease-1 in Birds

“…This is in contrast to what was seen in mammals, where both MASP-3 and MASP-1 mRNA transcripts were detected (Fig. 7, upper last lane) (20). Analyzing liver mRNA from other birds (including turkey, duck, goose, ostrich, and pigeon) on Northern blots suggested that the absence of MASP-1 may be a general phenomenon in birds (Fig.…”

“…4 and 6) (N. J. Lynch, unpublished observations). In contrast, the messages for MASP-1, MASP-2, and MAp19 mRNA are restricted to the liver in all species investigated to date, and those for MBL and the plasma ficolins are mainly expressed in the liver (2,20,24,45). The conservation of MASP-3 and its unique expression pattern suggest that its function may be decidedly different from those of the other lectin pathway components.…”

“…The cDNA probes used were: for the A chain of MASP-2, a 376-bp RT-PCR product amplified from chicken liver cDNA with primers M2A-ch-F and M2A-ch-R (Table I); for the B chain of MASP-2, a 430-bp RT-PCR product generated with primers M2dg-F2 and M2dg-R1; for the A chain of MASP-3, a 740-bp RT-PCR product amplified with primers M1&3dg-F and M1&3dg-R; and for the B chain of MASP-3, a 1200-bp NcoI fragment of clone CM3/5, encompassing the last 500 bp of the coding sequence and the first 700 bp of the 3Ј-untranslated (3ЈUT) region. For controls, rat liver RNA was hybridized with rat MASP-3 A and B chain-encoding cDNA probes, as previously described (20).…”

“…The mRNAs encoding MASP-1 and -3 are alternatively spliced products of one single gene. The A chain is common to both proteins, the B chain of MASP-1 is encoded by five or six exons (depending upon the species), and the B chain of MASP-3 is encoded by a single exon, located between the exons encoding the shared A chain and those coding for the B chain of MASP-1 (16,19,20). This genomic arrangement is found in amphioxus (a cephalochordate) and in all vertebrates investigated to date, but not in the ascidians, indicating that it arose after the divergence of the urochordates, but before the divergence of the cephalochordates (21).…”

Mannose-Binding Lectin (MBL)-Associated Serine Protease (MASP)-1 Contributes to Activation of the Lectin Complement Pathway

“…Murine MASP-1 (18) and MASP-2 (19) have already been cloned and characterized. We previously described murine MASP3 cDNA from the livers of C57BL/6J mice (20). In the present study, we generated MASP-1 and MASP-3 doubledeficient mice using a standard gene targeting method.…”