Interacting selectively and non-covalently with a hypermethylated cap structure consisting of 7-methylguanosine (m(7)G) followed by four methylated nucleotides (cap 4): 7-methylguanosine-ppp-N6, N6, 2'-O-trimethyladenosine-p-2'-O-methyladenosine-p-2'-O-methylcytosine-p-N3, 2'-O-dimethyluridine Such caps are known to be found at the 5' ends of SL RNAs of trypanosomatid protozoa.