C1 domain

{{Pfam_box

| Symbol = C1

| Name = Phorbol esters/diacylglycerol binding domain (C1 domain)

| image = 1ptr.png

| width =200

| caption = C1 domain of PKC-delta (1ptr)

Middle plane of the lipid bilayer - black dots. Boundary of the hydrocarbon core region - blue dots (cytoplasmic side). Layer of lipid phosphates - yellow dots.

| Pfam= PF00130

| InterPro= IPR002219

| SMART= C1

| PROSITE= PDOC00379

| SCOP = 2cpk

| TCDB =

| OPM family= 60

| OPM protein= 1ptr

| CDD = cd00029

| PDB=

}}

C1 domain (also known as phorbol esters/diacylglycerol binding domain) binds an important secondary messenger diacylglycerol (DAG), as well as the analogous phorbol esters.{{cite journal |vauthors=Azzi A, Boscoboinik D, Hensey C |title=The protein kinase C family |journal=Eur. J. Biochem. |volume=208 |issue=3 |pages=547–557 |year=1992 |pmid=1396661 |doi=10.1111/j.1432-1033.1992.tb17219.x|doi-access=free }} Phorbol esters can directly stimulate protein kinase C, PKC.

Phorbol esters (such as PMA) are analogues of DAG and potent tumor promoters that cause a variety of physiological changes when administered to both cells and tissues. DAG activates a family of serine/threonine protein kinases, collectively known as protein kinase C (PKC). Phorbol esters can directly stimulate PKC.

The N-terminal region of PKC, known as C1, binds PMA and DAG in a phospholipid and zinc-dependent fashion.{{cite journal |vauthors=Kikkawa U, Nishizuka Y, Igarashi K, Fujii T, Ono Y, Kuno T, Tanaka C |title=Phorbol ester binding to protein kinase C requires a cysteine-rich zinc-finger-like sequence |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=86 |issue=13 |pages=4868–4871 |year=1989 |pmid=2500657 |doi=10.1073/pnas.86.13.4868 |pmc=297516|doi-access=free }} The C1 region contains one or two copies of a cysteine-rich domain, which is about 50 amino-acid residues long, and which is essential for DAG/PMA-binding.

The DAG/PMA-binding domain binds two zinc ions; the ligands of these metal ions are probably the six cysteines and two histidines that are conserved in this domain.