Changes in Protein Function
Mutations can alter protein activity, specificity, stability, regulation, and interactions. Experimental studies allow researchers to trace some pathways between related protein functions.
The Investigative Question
How readily can existing proteins acquire different or expanded functions?
What We Observe
Proteins often tolerate some sequence changes while retaining function. Other mutations alter activity, binding, stability, specificity, or regulation. Experiments show that mutations can substantially increase weak secondary or promiscuous activities already present in a protein, sometimes allowing those activities to become increasingly specialized.
Scientific Background
Protein evolution can be studied through comparative sequences, ancestral reconstruction, mutagenesis, directed evolution, and laboratory selection.
Why It Matters
New protein functions are central to biological innovation because cellular structures and pathways depend upon proteins performing specific tasks and interacting with other components.
What Is Known
Protein functions can change through mutation. Laboratory studies have documented shifts in substrate specificity, catalytic activity, stability, regulation, and molecular interactions. Experiments also show that weak secondary activities can provide starting points from which mutations produce substantially increased activity toward a different substrate or function.
What Is Proposed
Evolutionary models propose several pathways toward altered protein functions. These include modification of weak secondary activities, gene duplication followed by divergence, recruitment of existing molecular interactions, and successive mutations that alter activity or specificity.
What Remains Uncertain
Experimental accessibility varies greatly among proteins. Demonstrating a pathway between related functions does not automatically establish the historical pathway for every protein family. The starting activity, number and order of mutations, effects on other functions, and availability of selectable intermediate states must be examined in particular cases.
Design Relevance
Intelligent Design discussions often focus on whether functional proteins are accessible through undirected sequence change. Experimental studies of actual proteins provide a way to investigate that question directly.
Assessment
Existing proteins can acquire substantially altered functions. Experimental studies demonstrate changes in activity and specificity and show that pre-existing secondary activities or molecular interactions can provide starting points for further change. The scale of the change, the starting function, the number and order of mutations required, and the availability of selectable intermediates should therefore be examined in specific cases.