1999 Nobel Prize in Physiology or Medicine
Reason for Award
for the discovery that proteins have intrinsic signals that govern their transport and localization in the cell
Laureates
United States of America
Explanation
Inside our bodies, each cell makes many building blocks called proteins. For a protein to do its job, it must reach the correct place, just like a letter needs the right address. Günter Blobel discovered that every protein carries its own tiny “address label,” called a signal. The cell has special helpers that read this label and guide the protein to its destination. For example, a protein meant to leave the cell carries a tag saying “send me outside,” while one that belongs in the nucleus carries a tag saying “go to the nucleus.” Thanks to this discovery, scientists better understand how cells work and can study diseases and develop new medicines.
Related Keywords
signal peptide
A signal peptide is a short 20–30 amino-acid sequence at the N-terminus of secretory and membrane proteins. It contains a positively charged N-region, a hydrophobic core, and a polar C-region with a signal-peptidase site. During synthesis, the Signal Recognition Particle (SRP) binds the peptide and pauses translation. The complex docks on the SRP receptor and transfers to Sec61, guiding the chain across the ER membrane. After translocation the peptide is cleaved and rapidly degraded.
Signal Recognition Particle
The Signal Recognition Particle (SRP) is a ribonucleoprotein complex that surveys cytosolic ribosomes. When it detects a nascent signal peptide, the SRP54 subunit binds and pauses elongation in a GTP-bound state. SRP docks on the ER-membrane SRP receptor and, upon GTP hydrolysis, hands the ribosome to the Sec61 channel. This rapid, accurate cycle minimizes targeting errors. SRP is evolutionarily conserved from archaea to eukaryotes.
protein translocation
Protein translocation is the passage of a peptide chain across a membrane via channels such as Sec61 or TOM/TIM. In co-translational pathways the chain threads through the channel while being synthesized, preventing misfolding. Post-translational routes rely on Hsp70 chaperones that keep the chain extended and drive insertion using ATP. The aqueous pore shields hydrophobic residues from the lipid bilayer. Failures cause cytosolic accumulation, stress responses, and disease.
endoplasmic reticulum
The endoplasmic reticulum (ER) is a cytoplasmic membrane network responsible for synthesizing secretory and membrane proteins, glycosylation, and calcium storage. Ribosomes attach to rough ER and inject proteins with signal peptides. In the lumen, chaperones such as BiP and PDI assist folding; misfolded proteins are cleared via ERAD. Processed proteins exit in COPII vesicles to the Golgi apparatus. The ER also triggers the unfolded protein response (UPR) to maintain cellular homeostasis.
nuclear localization signal
A Nuclear Localization Signal (NLS) is a Lys/Arg-rich motif that acts as a passport for proteins entering the nucleus. Importin α binds the NLS and, together with importin β, guides the cargo to the nuclear pore complex. Inside, Ran-GTP induces cargo release and the receptors recycle. Missing or mutated NLSs cause gene-expression defects. Viruses often exploit their own NLSs to gain nuclear access.
protein sorting
Protein sorting is the cell’s logistic system, using codes such as signal peptides and sugar modifications as barcodes to specify destinations. In the Golgi apparatus, pH gradients and lectin receptors partition cargos, adding a mannose-6-phosphate tag for lysosomal enzymes. Sorting errors can make digestive enzymes leak and damage tissues. Post-endocytic recycling and degradation pathways are also tightly regulated. Accurate sorting is essential for cellular function.
secretory pathway
The secretory pathway transports proteins from the ER to the outside of the cell, proceeding ER→Golgi→transport vesicles→plasma membrane. Quality checkpoints operate at each stage. In neurons and endocrine cells, cargos concentrate in granules for stimulus-dependent release. Pathway defects cause diseases such as diabetes and cystic fibrosis. Industry exploits this pathway in yeast or mammalian cells to mass-produce therapeutic proteins.
organelle targeting
Organelle targeting delivers proteins to mitochondria, peroxisomes, and other compartments. Because these organelles have little DNA, nearly all their proteins are nuclear-encoded and synthesized in the cytosol. N-terminal presequences are recognized by TOM/TIM or PEX receptors and driven inside by membrane potential or ATP. Reduced fidelity causes mitochondrial disorders or lipid metabolism defects. Researchers exploit the system to label organelles with fluorescent proteins.
protein misfolding diseases
Protein misfolding diseases occur when misfolded proteins lose function or aggregate into toxic species. Aggregates of amyloid-β in Alzheimer’s disease and α-synuclein in Parkinson’s disease are classic examples. Failed folding in the ER triggers ER stress and cell death. Trafficking bottlenecks revealed by Blobel’s work can worsen retention and aggregation. Therapeutic strategies now include chaperone boosters and small-molecule stabilizers.
biotechnology applications
Biotechnology applications harness signal sequences to mass-produce valuable proteins. By engineering a strong secretion signal upstream of an antibody or enzyme gene, cells release the product into the medium, simplifying purification. Adjusting glycan patterns further improves drug potency and stability. Synthetic biology now provides modular blueprints of the secretory pathway for environmental cleanup and microbiome engineering. Blobel’s concepts underpin these worldwide production lines.