| Modification Notes |
Lysyl hydroxylases (LLHs) 1-3 are hydroxylysines that function as attachment sites for carbohydrates. In collagen, the LLHs form hydroxylysine residues in -Xaa-Lys-Gly- sequences and are crucial for collagen crosslink stability. They form homodimers that localize to the endoplasmic reticulum. LLH1 is strongly expressed in liver, heart, lung, skeletal muscle and kidney tissue. LLH2 is highly expressed in heart, lung, kidney, eye, ovary and placenta, whereas LLH3 is expressed mainly in heart, lung, liver and testis. LLH2 exists in two alternatively-spliced forms: the long transcript (the major ubiquitously-expressed form) and the short transcript (expressed only in human kidney, spleen, liver and placenta). The long form of LLH2 is a bifunctional protein that plays a pivotal role in fibrosis by directing the collagen cross-link pattern. Any type of disruption of the regulation of the LLH2 transcript splicing may affect the stability of the extracellular matrix and contribute to specific connective tissue disorders. |