Part:BBa_K1660001

rMpL

K1660001

Introduction

rMpL has a good toxicity toward the nematodes. It is a novel lectin isolated from a kind of parasol mushroom (Macrolepiota procera). It is a kind of intracellular expression protein. MpL could bind with glycan of the nematodes specifically. So it can stop the growth of the nematodes from L1 phase to adults.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 125
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BamHI site found at 65
  Illegal XhoI site found at 151
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 208
  Illegal AgeI site found at 304
  Illegal AgeI site found at 519
  
• 1000
  COMPATIBLE WITH RFC[1000]

Structure

rMpL has a typical β-trefoil fold, consisting of α-, β- and γ- repeats (Fig. 1A). The β-trefoil fold seems like a tree, which has a short trunk (in red) and an expanded crown (in blue) (Fig. 1B). The trunk is a six stranded β-barrel composed of β-strands (β1, β4, β5, β8, β9, β12). And the crown is constituted by the other three pairs of β-strands (β2, β3, β6, β7, β10 and β11) and its connective loops.

Fig.1 Three-dimensional structures of rMpL in complex with carbohydrates.

Fig.1 Three-dimensional structures of rMpL in complex with carbohydrates. 1A: The structure of rMpL with a-, b- and c-repeats shown in green, cyan and yellow; 1B:The structure of rMpL in a tree-like orientation. The trunk is shown in red and the crown is shown in blue. Galactose is represented as sticks.

Function

According to the related literature，rMpL is toxic to C.elegans larvae. Only 20% of rMpL-expressing E. coli is sufficient to inhibit the development of most N2 larvae into adulthood(Fig. 2). The potential glycan targets in the nematode is ‘GalFuc’, for 30% of the worms developed to adulthood when nematodes lacks additional modifications in the antennae of N-glycans, and 20% of worms reach adulthood when nematodes lack the ‘GalFuc’ epitope in the N-glycan core, compared with almost all the nematodes which cannot reach to L4-adults with normal N-Glycans.

Fig.2 Toxicity of rMpL against wild-type (N2) C. elegans. Percentages in brackets represent the proportion of rMpL-expressing E. coli mixed with bacteria transformed with empty vector control. The dose dependence of MpL-mediated toxicity on development of L1 to L4 larvae is shown.

Design

In Macrolepiota procera, the MpL gene is 791 bp long (including start and stop codons) which is composed of four exons and three introns. By knocking out the introns, we will optimize this gene which comes from eukaryotic cells so that it can express efficiently in E.coli. Furthermore, we will add the pBAD promotor (BBa_K206000) induced by L-arabinose as well as the RBS (BBa_B0034) in the upstream of rMpL gene sequence, for pBAD promoter is suitable for the expression of the toxin. At the same time, the Xho I restriction site will also be added between the RBS and start codon, which will give us a lot of convenience to replace different promoter with different intensity. After acquiring the recombinant vector successfully, we will transfer the recombinant vector into the E.coli BW25113. Then we will design a series of concentrations of the L-arabinose to induce the expression of rMpL.

Results

After we successfully built the vectors, we transferred the vectors into different E.coli strains depending on the kinds of vectors. Vectors with pBAD promoter were transferred into E.coli BW25113. After rMpL gene was expressed in the bacteria, we did SDS-PAGE to testify the expression of rMpL protein. And according to the SDS-PAGE figure, we expressed rMpL in E.coli strains.

Fig.3 SDS-PAGE of rMpL

Lane 1, molecular weight standards (kDa); Lane 2-5, supernatant after 1.2, 1.2, 1.0, 1.0 uM L-Ara induction respectively; lane 7, supernatant after 0 uM L-Ara induction; Lane 8: supernatant of the pSB1C3; Lane 9, 10, 12, 13, 14: homogenate after 1.2, 1.2, 1.0, 1.0uM L-Ara induction respectively; Lane 15: homogenate of pSB1C3.

Reference

• [1] Sacchettini JC, Baum LG & Brewer CF (2001) Multivalent protein–carbohydrate interactions. A new paradigm for supermolecular sssembly and signal transduction. Biochemistry (US) 40, 3009–3015.
• [2] Jerica Saboti, Simon Zurga&Jure Pohleven(2014) A novel b-trefoil lectin from the parasol mushroom(Macrolepiota procera) is nematotoxic. FEBS Journal(UK)281,3489-3505.