Mutations inEFL1, anSBDSpartner, are associated with infantile pancytopenia, exocrine pancreatic insufficiency and skeletal anomalies in aShwachman-Diamond like syndrome.
For the final step of the maturation of the ribosome, the nascent 40S and 60S subunits are exported from the nucleus to the cell cytoplasm. To prevent premature association of these ribosomal subunits, eukaryotic initiation factor 6 (eIF6) binds the 60S subunit within the nucleus. Its release in the cytoplasm requires the interaction of EFL1 and SDBS proteins. In Shwachman-Diamond syndrome (SDS), a defective SDBS protein prevents eIF6 eviction, inhibiting its recycle to the nucleus and subsequent formation of the active 80S ribosome.



This study aims to identify the molecular basis of an SDS-like disease, manifested by pancytopenia, exocrine pancreatic insufficiency and skeletal abnormalities in six patients from three unrelated families.



Whole exome analysis was used for mutation identification. Fluorescence microscopy studies assessed the localisation of Tif6-GFP, the yeast eIF6 homologue, in yeast WT and mutant cells. Human and yeast EFL1 proteins, WT and mutants, were expressed inSaccharomyces cerevisiaeBCY123 strain, and circular dichroism and small-angle X-ray scattering were used to assess the folding and flexibility of these proteins. Green malachite colorimetric assay was performed to determine the GTPase activity of WT and Efl1 mutants.



Four patients were homozygous for p.R1095Q variant and two patients were homozygous for p.M882K variant inEFL1. Residue R1095 and M882 are conserved across species. Neither the GTPase activity of the mutant proteins nor its activation by the SDBD protein or the 60S ribosomal subunit were affected. Complementation ofefl1Δyeast cells with theEFL1mutants rescued the slow growth phenotype. Nonetheless, Tif6-GFP was relocalised to the cytoplasm in mutant yeast cells in contrast to its nuclear localisation in WT cells.



Mutations inEFL1clinically manifest as SDS-like phenotype. Similar to the molecular pathology of SDS, mutant EFL1 proteins do not promote the release of cytoplasmic Tif6 from the 60S subunit, likely preventing the formation of mature ribosomes.
Department of Pediatric Hematology, Oncology and Bone Marrow Transplantation, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.
Polina
P
Stepensky
Departamento de Química de Biomacromoléculas, Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México.
Montserrat
M
Chacón-Flores
Division of Genetics, Birth Defects and Metabolism, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, Illinois, USA.|Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Katherine H
KH
Kim
Nablus Speciality Hospital, Palestinian Authority, Nablus, Palestine.
Omar
O
Abuzaitoun
Departamento de Química de Biomacromoléculas, Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México.
Arnulfo
A
Bautista-Santos
Department of Medical Imaging, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.
Natalia
N
Simanovsky
Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Bari, Italy.
Dritan
D
Siliqi
Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Bari, Italy.
Davide
D
Altamura
Departamento de Química de Biomacromoléculas, Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México.
Alfonso
A
Méndez-Godoy
Departamento de Química de Biomacromoléculas, Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México.
Abril
A
Gijsbers
Department of Pediatric Hematology, Oncology and Bone Marrow Transplantation, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.
Adeeb
A
Naser Eddin
Pediatric Neurology Unit, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.
Talia
T
Dor
Division of Genetics, Birth Defects and Metabolism, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, Illinois, USA.|Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Joel
J
Charrow
Departamento de Química de Biomacromoléculas, Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México.
Nuria
N
Sánchez-Puig
Monique and Jacques Roboh Department of Genetic Research, Hadassah, Hebrew University Medical Center, Jerusalem, Israel.
Orly
O
Elpeleg
D001855:Bone Marrow Diseases / Q000150:complications / Q000201:enzymology / Q000235:genetics* / Q000503:physiopathology; D001842:Bone and Bones / Q000002:abnormalities*; D002648:Child; D002675:Child, Preschool; D010188:Exocrine Pancreatic Insufficiency / Q000150:complications / Q000201:enzymology / Q000235:genetics* / Q000503:physiopathology; D005260:Female; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014644:Genetic Variation; D006801:Humans; D007223:Infant; D008068:Lipomatosis / Q000150:complications / Q000201:enzymology / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D009154:Mutation; D010198:Pancytopenia / Q000150:complications / Q000235:genetics* / Q000503:physiopathology; D010445:Peptide Elongation Factors; D017510:Protein Folding; D017415:Ribonucleoprotein, U5 Small Nuclear; D054683:Ribosome Subunits, Large, Eukaryotic / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D000081003:Shwachman-Diamond Syndrome; D000073359:Exome Sequencing
C000599132:EFL1 protein, human; D010445:Peptide Elongation Factors; D017415:Ribonucleoprotein, U5 Small Nuclear; D020558:GTP Phosphohydrolases
Ribosome; Shwachman-Diamond syndrome; exocrine pancreatic insufficiency; pancytopenia