Our main area of research is the nanomechanical study of titin giant protein, which is responsible for the passive elasticity of muscle. We aim to investigate the effect of phosphorylation of titin protein on the structure of the polymer chain. In our experiments, we dephosphorylate titin molecules isolated from muscle tissue with a phosphatase enzyme and investigate the structural changes of titin molecules upon treatment. Our results show that the C-terminal part of the titin chain undergoes dephosphorylation and adopts a compact puffed up structure which is visible as a globular head region in atomic force microscopy images. This information allows us to understand how the degree of phosphorylation of titin induces changes in its structure at the molecular level.