BACKGROUND: Peptide aptamers are combinatorial protein reagents that bind to 
targets with a high specificity and a strong affinity thus providing a molecular 
tool kit for modulating the function of their targets in vivo.
RESULTS: Here we report the isolation of a peptide aptamer named swiggle that 
interacts with the very short (21 amino acid long) intracellular domain of 
membrane type 1-metalloproteinase (MT1-MMP), a key cell surface protease 
involved in numerous and crucial physiological and pathological cellular events. 
Expression of swiggle in mammalian cells was found to increase the cell surface 
expression of MT1-MMP by impairing its internalisation. Swiggle interacts with 
the LLY573 internalisation motif of MT1-MMP intracellular domain, thus 
disrupting the interaction with the mu2 subunit of the AP-2 internalisation 
complex required for endocytosis of the protease. Interestingly, 
swiggle-mediated inhibition of MT1-MMP clathrin-mediated internalisation was 
also found to promote MT1-MMP-mediated cell migration.
CONCLUSIONS: Taken together, our results provide further evidence that peptide 
aptamers can be used to dissect molecular events mediated by individual protein 
domains, in contrast to the pleiotropic effects of RNA interference techniques.