*4.2. Phosphorylation of the N2B Unique Sequence (N2Bus) Element of Titin Decreases Cardiomyocyte Passive Tension*

Functionally significant phosphosites have also been discovered within the I-band in the N2Bus. This is a positively charged region, therefore phosphorylation increases repulsion forces leading to elongation and softening of titin [84]. Kinases capable of phosphorylating this element include protein kinase A (PKA), extracellular signal-regulated kinase 2 (ERK2), protein kinase G (PKG), and calcium/calmodulin-dependent protein kinase II delta (CaMKIIδ) [17]. Dephosphorylation of the N2Bus has been demonstrated by protein phosphatase 5 (PP5) [85].
