Mutant/mutation
The mutant expresses a mutated version of IMC1a that is C-terminal tagged with mCherry. The N-terminal cysteine motif has been removed. Introduction of a diagnostic XhoI site changes the double cysteine (CC) in the amino-terminal motif to leucine-glutamate (LE)

Protein (function)
In Plasmodium eight conserved IMC1 protein family members have been identified, named IMC1a-IMC1h. Two of these, IMC1a and IMC1b, were shown to be differentially expressed in sporozoites and ookinetes, respectively, and to form part of their pellicle structures in P. berghei. IMC1a and IMC1b are structurally and functionally homologous and involved in parasite morphology, mechanical strength, gliding motility and infectivity, in accordance with their roles as membrane skeleton proteins (see also mutanst RMgm-147 and RMgm-148 lacking expression of IMC1b and IMC1a).
The zoites of Plasmodium, as well as those of related apicomplexan parasites, possess an unusual cortical structure termed the pellicle. The pellicle is defined by adouble membrane structure termed the inner membrane complex(IMC) situated directly underneath the plasma membrane, whichis equivalent to a system of flattened sacs or alveoli. On the cytoplasmic face of the IMC is anchored a network of intermediate filaments termed the subpellicular network (SPN), the function of which is to support the pellicle membranes and give the cell mechanical strength.
A family of proteins now termed alveolins have been identified as components of the SPN. In the genus Plasmodium, 13 conserved and syntenic alveolin family members have been identified that are dif-ferentially expressed among the three different zoites stages of malaria parasites. The alveolins identified in Plasmodium are characterised by having one or more highly conserved domains separated by regions of variable length and amino acid composition. Apart from the conserved alveolin domains, a subset of the alveolins also possess conserved cysteine motifs close to their amino- or carboxy-terminus. These motifs are made up of a single cysteine and a double cysteine that are separated by a small number of other amino acids. With the exception of IMC1i, The N-and C-terminal motifs are inverted, with the single cysteine located nearest the end of the polypeptide. The function of these cysteine motifs is largely unknown, although they have been suggested to provide sites for post-translational S-palmitoylation.
IMC1a is the only Plasmodium alveolin with conserved cysteine motifs at both ends, and in this study  site-directed mutagenesis and allelic replacement in P. berghei was emplyed to investigate the contribution of these motifs to the function of theprotein and the SPN as a whole.

Phenotype
Parasite lines IMC1a/mCherry-Mutant 1 displayed mCherry-based fluorescence in mature oocysts and sporozoites, as expected, demonstrating that the full-length IMC1a protein was expressed. However, in the mutant sporozoites the fluorescence levels were markedly lower compared to parasite line IMC1a/mCherry-WT (RMgm-1597) as a result of significantly lower (90%) IMC1a protein expression.

Microscopic examination of sporozoites from IMC1a/mCherry-Mutant 1 indicated that they had an abnormal shape (less severe than is the case after a complete knockout of IMC1a expression).

Salivary gland sporozoite numbers for Mutant 1 were consistently lower (10-fold) than those observed for IMC1a/mCherry-WT parasites (RMgm-1597)

Sporozoites did not infect mice after mosquito bite

Additional information
To study expression and localization of IMC1a and variants of it in the parasite, first  a transgenic P. berghei line was generated that expresses full-length IMC1a fused to a carboxy-terminal mCherrytag (RMgm-1597), named IMC1a/mCherry-WT. To study the contribution of the cysteine motifs to IMC1a function, mutations substituting the three cysteines were introduced by site-directed mutagenesis removing either the N-terminal motif (named IMC1a/mCherry-Mutant 1; RMgm-1598) or the C-terminal motif (named IMC1a/mCherry-Mutant2; RMgm-1599). The mutations introduced a diagnostic XhoI restriction site in order to screen targeting vectors and transgenic parasitesfor the presence of the desired mutation. Introduction of this XhoI site changes the double cysteine (CC) to a leucine-glutamate (LE). In addition, an IMC1a/mCherry targeting vector that contained a frame shift very near the 5' end of the coding sequence was used to generate a new IMC1a null mutant parasite line  (named IMC1a/mCherry-KO; RMgm-1600) using the same genetic approach as the other IMC1a lines.
In addition, two more mutants of the carboxy-terminal cysteine motif in IMC1a were generated, in which either its di-cysteine (named IMC1a/mCherry-Mutant 3) or its single cysteine (named IMC1a/mCherry-Mutant 4) were substituted

Evidence is presented that:
- The terminal cysteine motifs of IMC1a affect protein stability
- The terminal cysteine motifs of IMC1a affect sporozoite shape
- The terminal cysteine motifs of IMC1a affect sporozoiteinfectivity
- Properties of the carboxy-terminal cysteine motif aredetermined by the di-cysteine

Other mutants
See above