| Property | Summary | Key evidence/citation |
|---|---|---|
| Protein names | **CALR3** encodes **calreticulin-3**, also called **calsperin**, and has been described as a testis-specific homolog/counterpart of canonical calreticulin (CALR). | (pqac-00000000, pqac-00000005) |
| Primary molecular function and mechanism | CALR3 is a **testis-specific ER luminal molecular chaperone**. Unlike ubiquitous CALR/CANX, it behaves as a **lectin-deficient, client-selective chaperone** that directly supports maturation of sperm fertilization proteins, especially **ADAM3**. Its mechanism is not broad nascent glycoprotein lectin chaperoning, but selective assistance in folding/quality control of specific clients during spermatogenesis. | (pqac-00000000, pqac-00000002, pqac-00000016) |
| Substrate specificity | The strongest experimentally supported client is **ADAM3**; CALR3 co-immunoprecipitates with ADAM3 but not broadly with other nascent glycoproteins. In contrast, CLGN associates with ADAM1B, ADAM2, and ADAM3, whereas CALR3 shows much narrower specificity centered on ADAM3. | (pqac-00000002, pqac-00000003) |
| Subcellular localization | CALR3 functions in the **endoplasmic reticulum lumen** of testicular germ cells and is **soluble** rather than membrane-anchored, contrasting with the membrane-tethered chaperone CLGN. It is not retained in mature sperm, indicating its action is during biosynthesis/maturation rather than in the terminal gamete. | (pqac-00000000, pqac-00000016, pqac-00000010) |
| Tissue/cell type expression | Expression is **testis-specific** by Western blot and restricted to **germ cells**. Within the seminiferous epithelium, CALR3 is detected in **post-meiotic elongating spermatids**; studies evaluating myocardium found **no detectable cardiac CALR3 protein expression**, arguing against a primary cardiac role. | (pqac-00000001, pqac-00000005, pqac-00000006) |
| Temporal expression pattern during development | In mouse postnatal testis, CALR3 appears at about **3 weeks of age**, later than CLGN (~2 weeks), consistent with **post-meiotic/haploid expression** during spermiogenesis. This timing parallels its specialized role after meiosis in elongating spermatids. | (pqac-00000001) |
| Key interacting partners in the pathway | Core partners include **ADAM3** (direct client), **PDILT** (forms a CALR3/PDILT quality-control module for ADAM3 folding/disulfide maturation), and functionally linked factors such as **CLGN** and ADAM1A/ADAM2 upstream in the broader ADAM3 maturation pathway. Recent work also places CALR3 in reproductive protein networks with **PRSS37**, and proteomic/genetic studies implicate linkage with **TEX38/ARRDC5/PDILT/CLGN** modules affecting ADAM3 maturation. | (pqac-00000010, pqac-00000016, pqac-00000007) |
| Biological processes/pathways involved | CALR3 acts in a **specialized ER protein quality-control pathway during spermatogenesis** that enables proper **ADAM3 maturation**, sperm surface competence, **migration through the uterotubal junction/oviduct**, and **binding to the zona pellucida**. This pathway is part of the molecular program that generates sperm fertilizing ability. | (pqac-00000004, pqac-00000010, pqac-00000013) |
| Phenotype when disrupted (knockout studies) | **Calr3-null males are infertile or nearly sterile** despite apparently normal spermatogenesis, normal sperm morphology/motility, and normal mating behavior. The main defects are **failure of sperm migration from uterus to oviduct/UTJ**, **impaired zona pellucida binding**, and **loss of ADAM3 from mature sperm**. Fertility can be rescued transgenically, supporting on-target causality. | (pqac-00000004, pqac-00000003, pqac-00000002) |
| Clinical relevance to human disease | Current evidence supports CALR3 primarily as a **male fertility gene/protein**, relevant to unexplained fertilization failure and potentially to contraceptive target discovery. By contrast, a large 2018 human genetic/pathology study found **no convincing evidence that CALR3 is a monogenic cardiomyopathy gene**, noting lack of myocardial protein expression and non-supportive segregation data. | (pqac-00000005, pqac-00000006, pqac-00000007) |


*Table: This table summarizes the key biochemical, cellular, developmental, and clinical properties of human CALR3/calsperin. It emphasizes the experimentally supported role of CALR3 as a testis-specific ER chaperone in ADAM3 maturation and male fertility, while noting evidence against a primary cardiac role.*