A 50 year old lady is given methotrexate for severe rheumatoid disease causing joint pains and functional limitation. She also has to be given folinic rescue therapy. Which of the following is the mechanism by which methotrexate acts?
Binding to dihydrofolate reductase
Increasing folic acid excretion
DNA binding
Binding to dihydrofolate reductase
Increasing nucleotide synthesis