[ccp4bb]: Confusing N-terminal density

[Neil Paterson]

Dear all, I'm currently puzzled by some N-terminal density visible in a 1.4 angstrom map (image).  My protein has been cleaved with 3C protease, cleavage confirmed by SDS-PAGE and failure to rebind a NiNTA column.  3C should cleave LEVLFQ/GP yet there appears to be strong density preceding the glycine.  The density is not a great fit for an additional residue (although there shouldn't be one) and I'm sure my glycine is in the correct place as the proline density is very clear. Has anyone seen anything like this before or have any suggestions as to what it may be (and how to model it)? Thanks, Neil